The map may crash minecraft on opening because of its pure size. So I recommend to change the JVM-Arguments to at least: -Xmx4G -Xms4G (=4GB RAM, that is what I use).

The map was tested in Minecraft 1.12.2. It is highly recommended to also use 1.12.2 to play this map. ;)

In case you still run into performance-issues, here is a version of this map where all redstone-clocks are off, so the map should run much more smoothly.

As a tribute to Emily who got lost in this city, here is some guidance to prevent such fate: xD

Coordinates: 800,63,976 will teleport you right back to the Southern Gate.

Message-System: Search a manufactory of your choice (e.g. the Cattle Farm is very close to the southern gate). Request an item, until you get the "is empty"-message. If you click the manufactory name in this message, you will get teleported back to this manufactory. So you can start exploring with this message in your chat, being only one click away from a manufactory you know.

Main-Streets: Each ring has a main street running around the entire city and marked with endstone. If you stick to those main streets and explore the city ring by ring you should be able to see a lot of it while always knowing where you currently are.

Spectator Mode: Switching to Spectator Mode and fly up will always help.

The wall isn't only shiny and massive. To make the wall working in real survival gameplay, it is enforced with a layer of obsidian inside. Before the obsidian layers of water can be found to make mining more difficult. Together with the enclosed lava columns, the wall has a build-in cobblestone-generator, regenerating the internal cobblestone-columns almost instantly, making it nearly impossible to mine through in survival. And thanks to the water it is TNT-proof also.

City Wall Profile

The giant gates of the eastern and southern wall protect the city from unwelcome intruders. These massive gates are actually functioning. Each gatehouse owns two gates. Depending on the gate-mode the gates can either open alternately to enforce a checkup on all incoming or outgoing travel. Alternatively, the gates can be opened or closed independently so large groups can enter or leave the city unhindered. The gate-mode can be chosen at the inner gate.
The gates can be controlled from ground level or at the top of the gatehouse. To enable or disable the energy-bridge spanning the moat, you can use the bridge-control at the top of the gatehouse.
If you find yourself inside the moat, look for these eastern or southern entrances, there are ladders on the outer wall so you can get out.

Overground city wall and open gate

The Ocean Gate at the outer northwest wall does not only open and close, it also raises or lowers a bridge to form a canal so ships can enter or exit the city. The gates can be controlled from the outer harbor or from the top of the gatehouse.
When opening the inner gate, the flashing canal lights are leading the ships into the harbor at the Middle Ring.

Closed and open Ocean Gate

Not all entrances to the city are above ground. There are four underground gateways, one in each of the four cardinal directions.

Closed and open underground city gate

Above each underground city gate is an underground railway station. The railway moves counterclockwise around the entire city. So pick your destination and grab yourself a minecart at the station. There are not just boring tunnels, I promise. If you manage to lose your minecart, watch out for buttons on the walls. They open secret passages to leave the railway tunnels.

North underground railway station, a railway tunnel and tunnel going past the south station

The City Wall hosts 16 Force Shield Generators. Each one can shield a certain segment of the city. All generators together (including the one at the top of the Palace) are able to enclose the entire city in a nearly impenetrable force shield. Each generator requires fuel, which can be any item. As long as fuel is provided, the generator can keep its shield active. The shield vanishes, as soon as the generator is deactivated or runs out of fuel.

A Force Shield Generator in deactivated and activated state. The generated shield can be seen on the left.

In this district cows and chicken are domesticated, to obtain meat and other resources from them. There is the dairy farm for milk. Next to it is the henhouse with a chicken auto-brewer. The auto-brewer has two modes, so you can choose if you want your chicken cooked or raw. Below is the slaughterhouse for fresh beef. A special feature of the slaughterhouse is the countdown timer, which can be started each time a pair of cows was set to love-mode. So, you can easily see which pair of cows is ready to enter love-mode again, and when. At least we have the brazier here to cook all the raw meat and get it well done to the central storage (see below).

Dairy Farm and Henhouse

The military district is dedicated to enforce law and order in the city and the whole kingdom. The barracks with their armory is located here, as well as the training courts for melee and range combat. In each training court you can choose the difficulty you want to train and get experience as reward for a successful training. Under the barracks is the dungeon with more than 100 cells for all kinds of villains and criminals. The stables and a small paddock are also part of this district.

The Barracks, Drill Ground and Dungeons

The agricultures provide the citizens with all kinds of vegetables, each one cultivated at its own farm. Needless to say, the melon and pumpkin farms are fully automated. The fields of the wheat farm can be harvested automatically each one on its own. The two windmills can be activated to spin in the wind, thanks to command block magic.

Carrot Farm and Wheat Fields

In the north are the great corridors deep below the water surface. Apart from these celtanean architectural master pieces, this district mainly consists of living quarters. Most of them grant a spectacular view at the submarine wildlife. At the bottom is the Sandpit, where sand is quarried to supply the celtanean glass kilns.

District overview and inside of a deep-sea corridor

Above the Deep Sea Corridors hovers the Floating District. This district is dedicated to Elytra and features the Elytra Workshop and the Repair Station. Apart from those manufactories the Launch Tower arises high in the air to provide a proper start platform for an elytra glide. Elytra and Fireworks can be obtained at the base of the tower.

District overview, Elytra Workshop with Launch Tower and Elytra Repair Station

West of the Deep Sea Corridors you can find the submarine district with its great halls and underwater living quarters. It extends from the north-west to the south-west of the Outer Ring. First, we have the squid tank here, where squids are hunted by domesticated guardians for their ink. The great sugar cane silo, the smoke house and fishing docks are also located here. To grant access to the canals of the Middle Ring, we also have a (functioning) lift lock here, which connects the port entrance with the lower canals of the inner city.

Northern and Southern Submarine District

In the south-west we find the botanic district which extends into the south-west of the Middle Ring. The tree nursery, the sawmill and carpentry are located here. In the Middle Ring's part, you will also find parks with fountains where you can chill and relax.

The Park (Middle Ring) and Tree Nursery (Outer Ring)

The south-east Middle Ring is dedicated to the hard working Celtaneans, having all their workshops distributed across the 3 floors of the Ring. The Ropeyard, Shears Manufactory, Glass Kiln, Bowyer's Workshop and many other facilities are located here, producing nearly every item used for everyday life. Between all the workshops you will find the houses of those busy craftsmen, living and working here.

Bowyer's Workshop, Name Tag Workshop and Gold Macerator

In the north-east of the Middle Ring you will find the District of Scholars, expanding up to the Inner Ring. This is a place of wisdom and knowledge, where all the incredible technology of the Celtaneans was researched and developed.

Sanitarium: Coming from the workshops, we have at first the Sanitarium for the sick and ill. In the center there is a (functioning) healing chamber to cure all physical pain instantly and for free. If you feel exhausted or stressed, feel free to pick a bed and stay there for a while until your mind is refreshed.

Grand Library: Next to the Sanitarium is the Grand Library. Each floor of the library is dedicated to another topic (tools, armory, weapons). In one of the library's lower rooms you can enable the enchanted-books feature. With that feature enabled, nearly every chest in the library has a small chance to have an enchanted book in it, fitting the floor's topic. On the 4th floor you will find anvils and enchantment chambers to enchant your tools and weapons.

Observatory: On the Inner Ring of the scholar's district, we have the Observatory which activates itself at night and then grants a small glimpse into the depths of the galaxy out there. So go up the high eastern tower and look through the telescope to try it out yourself.

Academy: The Academy is the large building, connecting the Lower City with the Inner Ring. The Academy is a building of great knowledge and easy learning. As long as you stay in the Academy building, you will gain a small amount of experience, if your level is below 10. This feature can be toggled at one of the upper two lecture halls.


Sanitarium, Grand Library and Observatory

The Harbor of Celtanis lies in the north-west. It is connected via a canal with the Ocean Gate. In the Harbor itself the shipyard is located. Inside the harbor district there's a lot of living space for all of the seamen sailing the oceans. In between you will find the harbor warehouse. At the end of the warehouse there's the "Stacking Chest", which stacks none-stackable items so the seamen have more room aboard during their journey.

Docks, Shipyard and living quarters

The entire west Inner Ring is the Brewing District. This is the place where the caltanean alchemists mix their potions. All kind of strange laboratories can be found here, where all the ingredients for those potions are manufactured. At the west we have the great hall of brewing with it machines, where potions can be auto-brewed by everyone.

West and south Brewing District and the Brewing Hall

The south-eastern Inner Ring contains the workshops of the engineers, dealing with physics and explosions. Next to their workshops and living quarters you will find a TNT-Cannon (working of course) and a full laboratory to build all kinds of fireworks (including a tower to launch them).

Tinker Town Overview, Watchmakery and Fireworks Laboratories

At the top of Celtanis rises the Palace in all its glory. Its hanging gardens and large halls has given home to the royal family for hundreds of generations. On the eastern wing of the Palace you will find the court, where justice raises its voice and fair sentences are passed. The celebration hall is located at the west wing, where large festivities take place. The throne room can be reached if you enter the city through the South Gate and walk right ahead all the way up.

Palace at night, court and celebration hall

The four towers of the Palace are all mighty machines. The grand symbols at the top of each tower indicates what the machine's power is.

	South East Tower (Eye): The tower at the south-east contains the "Astral Manipulator". You can use it to gain an astral body (=Spectator Mode) to move through the world freely. If you want your old body back, simply fly to the upper chamber of the tower, where the process will be reverted.
	North East Tower (Command Block): The north-east tower is the "Command Tower". It uses the power of Energy Crystals (explained later) to change global conditions, like Fire Ticks or Mob Grieving. You can even disable Ender Pearls or TNT here. Each action of this tower consumes energy, so make sure you have a bunch of Energy Crystals ready if you want to use it. It also has an energy reload system which automatically refills Energy Crystals, as long as you have some in stock.
	North West Tower (Cloud and Ligthning): This tower contains a weather manipulator. Climb up all the stairs to the top chamber to enforce the weather you want and choose how long you want it.
	South West Tower (Sun and Moon): The tower at the south west corner of the Palace contains a time freezer. Choose any time of the day that you want the world to be frozen in. Alternatively, you can also unfreeze time here. Watch the water stream at the center of the tower. It will tell you if time is currently frozen or flowing.

At the north of the Palace floats the Sanctuary, only connected to the rest of the city by a bridge of energy. Legends say, it once came done from the heavens and the city was built to reach it. More serious historians are sure the Celtaneans are pretty able to build floating structures, and dedicated this one to worship and praise their one God.
In the bottom area of the Sanctuary you will find the living quarters and teaching rooms of the priests and novices. At the top you will find the Temple itself, fully diamond plated and dedicated to the one almighty God. You have to push the correct button to get access to this holy place. (I'm myself a Christian, so no surprise that you will find some kind of cross in there ;))

Sanctuary overview, the entrance hall and a lecture room

Below the Palace, at the bottom of the city, you will find the Great Pyramid. With its large stairs and waterspouts, it is the cultural center of Celtanis.

Shop: In the lower outer corridors a shop system can be found, where you can buy items using your levels. Feel free for a shopping tour, if you can raise all the experience it takes. If you have none, a sell-system offers you the opportunity to sell 8 items to gain 1 XP.

Storage: At the upper level, the central storage is located. It comes along with an auto-sorting system and digital storage technology (scoreboards), allowing to store 2,000,000+ items of each type. All items of the celtanean supply chain are supported. Each manufactory receives their items (and sends their output) to this central storage.
Click the button below an item to get one out of the storage. If you want an item to keep in storage and don't be used by a manufactory, you can lock it.


Great Pyramid Overview, Pyramid center, storage and shop corridor

At the Technical Level most of the command blocks and be found, running the 3 big system of the city. Here you can toggle the storage system, the message-teleporting system and also the district name system. All involved entities will be removed and the corresponding clocks get stopped. This may help you, if you run into some performance issues. To enter this hidden area, follow the endstone from the pyramid center. You will notice a pressure plate at the floor at the left wall (left of the dump). Step on it and a secret passage will open to the Technical Level (a similar entrance can be found when leaving the pyramid to the north).

Storage mainframe and secret entrance to the Technical Level

If you enter the Underground through the southern stairs and turn right, you will find the entrances to the Great Forges on the outer walls. There is a southern and a eastern hall. Each one contains six individual forges, where all kind of tools and armors are crafted.
Between those halls, you will find a great cave with the living quarters for all the hardworking blacksmiths and their families.

One of the two Great Forges Halls and Horse Armor Forge (Custom Crafting)

In the north eastern corner of the main underground cave, you will find multiple entrances to the Mines. Beside an enchanting room, you will find multiple "Ore Generators" in the mine shafts. Each generator will be able to create one kind of ore from pure energy.
Once charged with an Energy Crystal (see below), the generator can run four times, generating a random amount of ore, which then can be mined. The amount of ore per iteration depends on it minecraft given rareness. So, you will get less diamond ore from the Diamond Ore Generator then you will get coal from the Coal Ore Generator. The generators itself are located vertically relatively to the y-level an ore is found at. So, the Coal Ore Generator will be found on the highest level, where as the Diamond Ore Generator will be found at the lowest.

Mines and a mine shaft

In the north-west part you will find large ravines, full of lava, covered in a complex system of pillars and bridges. These part of the city was highly inspired from this thread (so let me give credit here).

Mushroom Farm: In this area you will find the fully automated mushroom farm in the north.

Nether Wart Farm: In the west is the nether wart field, which can be automatically harvested by button press.

Crystal Forge: If you go downstairs one the left or right at the long road heading west, you will find the Crystal Forge. This is the place where Energy Crystals are forged (using some custom crafting). The Energy Crystal is a special item, which is the celtanean way to store energy. Every time a special action should take place (Generate a resource, use Command Tower, Assemble Squids, etc...) an Energy Crystal is required. These crystals are crafted here, stored in the Storage (as any other item) and can be requested from every place needing one.


Molten Ravines, Energy Crystal Forge and Nether Wart Farm

In the south-west corner you will find the entrance to the great Arena. In the bottom level, you have an armory, a brewing room, a regeneration zone (with food and healing chamber) and a respawn room. Once activated, you will find the monster selection in the side corridors. Pick the monsters you want to fight and enter the Arena through the northern door. The monsters will wait for you behind the southern door, which opens when you close the northern one.
You can also change the Arena itself in the south western control room. Choose from "Default", "Desert", "Nether", "Spleef", "Ice" and "Pool" and fight in the surrounding you like.

Arena with default and nether battleground, mob selection

Deep in the Underground, behind the great Arena, lies the Zoologic District. You will find a themed "cage" for each none-human monster here, so you can study them in their natural habitat. If the monsters vanished (because you changed difficulty or for any other reasons), you are free to push the buttons at the cage, to respawn them. You will find Creepers, Zombies, Spiders, Cave Spiders, Skeletons, Shulker, Endermen, Endermite, Slimes, Ghasts, Blazes and Wither Skeletons here.

South and west Zoologic District

Following all stairs beyond the lower underground level, you will find the catacombs in the deep center of the city. The loved ones of the Celtaneans are buried here in their coffins. Over all three floors you will find corridors full of silence, memorial and lament. Starting at the small chapel at the great south western pillar, a died Celtanean find his last peace here. So be respectful when you wander through these halls and gets the kids out, which use a sprint through the upper hallways as their childish test of courage.

Catacomb rooms, corridors and center

At the underground center, in a pool of lava lies the Core. A pulsing beacon of light and energy which reaches from down here all the way up to the Palaces' roof. Feel free to spend some resources to unleash the area effects.

Core of Celtanis with the beacon running through the entire city

Deep below, throughout the whole city are the endless canals and rooms of the Waterworks. It seems this maze of water leads from everywhere to everywhere. Ensure you do not get lost in the large canal system of Celtanis. You would not be the first. Once you know this labyrinth, you can use it to get from one location to another quickly.
And if you fall into one of the many lava pools and make your way to the exit somehow (every lava pool has an exit!) it is very likely you will find yourself here. So good luck on your way back to the main streets of the city.

Tunnels of the Waterworks

Along with the districts above, which are explicit mentioned and having their own name, there is a lot more in underground, which is worth to be mentioned:

	Blast Furnaces: In the south-east corner the Blast Furnaces are located. These mighty ovens smelt gold or iron to ingots using actually small furnaces in them. At the control panel of each furnace you can adjust which ore the furnace should melt and which fuel should be used. You can also use the manual fuel input, if you have some own fuel at hand. At the feet of every Blast Furnace a lever can be found, which clears all fuel inputs and forwards them directly to the output chest. Just in case a none-fuel item blocks the Blast Furnace.
	Golem Factory: Next to the Blast Furnaces at the south lies the Golem Factory. It can be reached by the hanging stone bridge across the lava pool. If you have enough iron blocks and pumpkins in store, this factory actually produces Iron Golems. Smash one of the buttons to test it. But there is more. Once an iron golem is produces, it reaches the collection chamber at the lower level. Go down there and ensure the lamp on the right about the switch is lit, to have Golemancys activated. If you press the button on the left, the essence of one of the golems is bind to the book, given to you. If you read that book and press the corresponding text passage, the contained golem will be freed at your current location. This way the factory does not only allow you to produce golems, it also enables you to take them with you and place them, wherever you want.
	Dimension Portals: At the west stairs leading to the lower underground level, you can find the entrances to the portal rooms. The Nether portal on the left can be toggled on/off by using the button. Use the switch to activated the auto defense against some pert Pigman, coming through the open portal. The end portal room on the right has no special abilities, apart from the fact, that the pressure plates set your spawn point at the floating platform at the end of the room, to have an atmospheric point of arrival, once you come home from the end.
	Monster Trap: At the west outer wall of the main underground camber, there are the entrances to the Monster Trap. The trap itself is simple and relies on the fact, that monsters do mention open trapdoors as full blocks and fall to their death. In case some super clever skeleton spawns with feather falling boots, some golems waiting at the bottom to finish them off. Use the large leaver at the northern wall to switch the trap on or off. If you somehow managed to fall into the killing zone, you will find a button at the back wall on the right, opening an exit for you. In case you are impatient, there is a "Kill all" button on the southern wall, which will teleport all mobs in a location, where they will fall down from there platforms for sure. Once activated, you have to wait for the cooldown to finish to use it again (would be pretty imba otherwise ;) )
	Monster Spawners: Left next to the Arena are the Monster Spawners for all kind of monsters which drop relevant resources for the city. Each of them is toggleable and designed to get a good killing rate at minimal danger. Even Ghast can be spawned and slaughtered, using the huge hall in the south.

There are a lot of lava lakes, pools and pits in the underground. And you might manage to fall in one of them. If you do, do not panic: each single lava pit is carefully designed to have an exit, so you're not doomed to die in it. Maybe sometimes it is futher away, so some fire potions might come in handy. But if you look close enough, you'll find it. If you think you've found a lava pool without exit, please let me know.

Throughout the whole city you will find a lot of different facilities, each equipped to produce a certain item. Celtanis supports a supply chain of over 100 items. Click the image below (5 MB!) to get a detailed diagram which facility requires and produces which item. You will find these facilities in their corresponding districts.

A message system tells you, whenever an item is locked or out of stock. The cyan parts of the messages contain tooltips, so open the chat and hover over them with the mouse. Whenever you see the gray text "Click to teleport there", you are able to click the cyan part and teleport to the corresponding location instantly (Be aware that the message source itself often also offers an option to teleport you back to it). This way you can move around in the city quickly if any item is missing and you want to craft it fast at the corresponding manufactory.

Message with teleportation tooltip

If you went through the city carefully, you may have noticed the white portals every here and there. These portals lead to another dimension, the Nexus. Each of them has a unique shape, which matches their corresponding counterpart in the Nexus.
In the Nexus all those portals are arranged to each other the same way they are in the city. But the distances between them are heavily reduced. So, use the Nexus if you want to get from one end to the city to another in nearly no time. But do not fall off the platforms. There is no ground here.

A Nexus Portal and the Nexus Hub itself

All over the city Taverns are present. Every Celtanean who is hungry or wants to sit down with his friends for a talk is welcome here. Just get to the bar and order the food you like. Also check out different Taverns, because the menu differs between them. Look out for the tavern sign on buildings to find a tavern near you.

Tavern with sign and Tavern rooms

Beside all the buildings above, I want to mention some other more technical features of this build.

Spawnproof: The whole city is lit up. No Mob should be able to spawn anywhere. An exception are Slimes. There is a small clock at the Technical Level to get rid of them. Same for bats (which I find just annoying)

Copyable: This city is not only offered as download, it is designed to be copied from this world in any other world you like. All command blocks work with relative coordinates, so feel free to include this build in your world. Please give credits, if you do so.

Multiplayer: All commands and features are designed to work also on servers, Every command was carefully written using triggers, to prevent all players using those features must be admins.

Adventure Mode: To make the city even more useful, it is adventure-mode friendly. Whenever you get a tool from the storage system, it has the corresponding tags on it, to actually work in adventure mode. So you are able to break ore with your pickaxe, but not the walls of your house. ;)

No Resource Pack: I think minecraft has developed far enough, where the absent of needing a resource pack has become mentionable. The whole city was built in vanilla without any resource pack. So no extra downloads, if you want to roam the city. (Ok, actually I used a small one to correct the top texture of upside-down stairs to fix MC-57935)

Turn it off: Every feature requiring entities or a clock to work (storage, shop, etc...) can be shut down. So nothing will going on, if you do not want to. Also useful when facing performance issues.

You are totally allowed to use this city on your server, as long you give credits and link to this project side. To make Celtanis fully work on another map, please follow these steps:

1) This map was built in 1.12.2 and was tested in this version. So, you want to run minecraft 1.12.2. on your server to be sure everything works.

2) Shut down all systems working with scoreboards

3) Teleport to 787 44 779. Although this command block works with relative coordinates, the armor stand has to be spawned in always loaded chunks. Otherwise the storage system will not work. So ensure it does, once the map was copied.

4) Copy the city in your server map with the tool of your choice

5) Ensure the command block mentioned in 3) is adjusted accordingly.

6) Enable all scoreboard-systems mentioned in 2)

7) Done. Enjoy Celtanis on your server.

I'm aware no server nowadays runs without plugins. Because I'm not a server owner myself and have no experience in running a server, I cannot support you further then here. If any problems occur, I'm afraid you have to solve them on your own.
But please let me know your solutions nonetheless. This way I can check if the problem could be avoided using vanilla mechanics and link your solution to other server owners facing the same problem.

Documentation:
I threw together all files I used to plan this build, added some documentation and zipped them. So if you are interested in the technical backgrounds you're welcome to have a look into it. You'll need Microsoft Word (.doc, .docx), Microsoft Excel (.xls, .xlsx) and yEd to open all files. If you feel like some important aspects are missing, please let me know.

Celtanis Documentation

Archive
This map has its own history since it was first published. There were older versions of the map, created for older minecraft versions. So for everyone being nostalgic here they are:

Minecraft-Version	Download	Off-Version
1.9.2	Celtanis for Minecraft 1.9.2	N/A
1.11.2	Celtanis for Minecraft 1.11.2	Off-Version for 1.11.2

Because this map is very complex and minecraft itself is not bug-free, you may run into some issues, which cannot be prevented yet. I know about those and will fix them once they get fixable:

• Storage-Messages - Currently Storage-Messages showing multiple times for one player and never for all others in multiplayer - This needs 1.13 commands to get fixed reasonable. So once the city get updated to 1.13 I will fix it (which may take a while, because 1.13 has changed A LOT and tools have a hard time supporting 1.13, e.g. see here).
• Instability since 1.12 - As this map was updated to 1.12, it seems to crash minecraft from time to time now (wasn't the case in 1.11). I've absolutely no idea what I could do about that. Sorry for this in advance, if it happens to you. Hope it fixes itself when updating the map to 1.13+. If you have any suggestions why this is or how to prevent it, please let me know.
• Lift lock kicks players out of boats - Unfortunately MC-102608 and MC-97513 are not fixed yet. So, teleporting the boat and player upwards together seems to be impossible for now. Strangely the boat only gets teleported up by 1, so none of the bugs seem to match properly. The only workaround to prevent the boat from sinking is to make the player leave the boat and swim up himself. Sorry for any inconvenience.
• Items does not stack - Sometimes items of the (seemingly) same type do not stack. This is not a bug. Because all items dispensed by the city are usable in adventure-mode, those items may not stack with items crafted or gained by the player. Therefore it is always recommended to put items, which are supported by the city, into the storage. When requsting items of that type from the storage again, you'll get the adventure-mode friendly and stackable version of it.