Thar, sneaked in a "funded" project (meaning I spawned my ass off). It's a small building on the surface with a ladder and staircase extending down to bedrock.

There is an open cave at the bottom, 20x20x6, with a ladder connecting to another 2 such chambers above it. I cheated a bit and used a tool to figure out where a slime-spawning chunk was near spawn and centered those chambers in it. Since slimes are so hard to find, it's nice to have a place where you know they should be spawning.
Seems to be working.
Crap.
I'll be prettying it up a bit, but it's functional.
All the ill-gotten gains I dumped in the chests at spawn, free for the taking. Some good stuff there imho, mostly cobble though.
Also:

Neat.