It took a while to draw the maze, somewhere in the maze there is an extra big room.
In that room you can put whatever you want to make an adventure on a multiplayer map.

What it have,
* a very hard widling way to the room of your desired action
* unbreakable walls, no cheeting for contestants

What it does not have until you put something there
* Redstone traps
* Spawn cages
* Amazing objects

I can see two uses
* Just a part of a quest
* A broadcast that there is something valuable in there and then the online group have to race to find it first.

Additional Notes

If you just ad it to your map without peeking there is something small inside already

How fun is it to see a gray square, because that is how it looks on the outside.
I will upload the sky-scrape schematics later (seen on the photo)