The backstory: When the lands became ruined by a virus, the 'overlords' built 13 towers and remove the land as far as the eye can see (Literally). First they build the 'trial', to keep order. Then the homes for the poor and the shops to provide. After that came the houses for the average citizen and the mansions for the 'importants'.

12 of the towers fell (both literally and metaphorically) because they could not survive the lifestyle. Tower 13, however, was under heavy control and survelliance.

Although it was frowned upon, the 'overlords' were forced to build connections to the outside land, although these were blocked off by one way gates, out of the city.

etc. etc.

The lowdown: A tower floating over nothing, connected to land via 4 bridges (One of which is badly damaged). The tower itself does not allow access to outsiders and divides it's population into 4 ranks.

Rank 4: The upper class people, living in mansions.
Rank 3: Middle Class people, living in houses.
Rank 2: The lower class/working class, populated with hobos and shops.
Rank 1: Prisoners, sent to the 'trial'.

Trial: Cubes connected to cubes connected to cube. Fairly safe by day, swarmed with mobs at night. (Also: an odd amount of slimes spawn by day). Prisoners are sent to this 'labriynth' and either die or manage to get out safely (There's one official exit, but many other ways to get out, but they won't get you back to the tower).

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Running through the trials at day = Fun to find the occasional slime and easy to navigate.
Running through the trials at night = REALLY creepy. (Especially in 3D, I just had to try.)

Trial has been finished, but I feel there isn't enough mobs spawning at the moment, so feel like throwing in a few mob spawners. I also feel I should add treasures and 'safe' rooms (lit by torches). I'm also thinking of throwing in a few NPC's, to add story (if I find out how).
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Blah blah blah.

Additional Notes

Texture pack used: Tronic (But it also looks fine in Default).
Mods used: SSP Commands(World Edit), FlatWorld (Althought this was completely unnecessary).

Currently working on: Finishing the trials. This includes running through it a few times at night to explode a few creepers, to give it that 'many have died before you' feel. ;D