...that is no longer secret because I am showing it here!
Since I joined the server three days ago, I have been underground digging away at the smoothstone that lay underneath all that grass, creating something. Progress has been slow due to hitting 3 lava lakes, 2 encounters ending in death. One because I dug into the bottom of it and the other a Skeleton shot me into it as I was filling it with gravel.
Anyway, it is still heavily in development, a bit messy in some places, such as staircases, but I have ensured that the biggest bits are at least dug out and are cleared of rubbish and smoothstoned over.
You'll probably guess from the pictures, but for those who don't, it's a Fallout 3 inspired underground vault.
Atrium with window into/out of Overseer's office, corridor and cafeteria (far left)
Looking down one of the three apartment corridors (soon to be more on the lower levels). All corridors with apartments have showers at the end
Security, currently the only furnished room in the vault.
Small reactor room (water purification is just through the door)