History of the server being the topic, there is a place in the city:
Below it are extensive dungeons with redstone circuitry, lava pillars, and other broken, incomplete, or just not obvious machinery.
What is this place?
That was my spawner/mob grinder project. There used to be signs labeling things, but evidently not anymore. The lava pillars were a system of entirely disabling the spawning floor all at once, in order to stop mobs from spawning for any reason.
Project was abandoned due to zombies having a small amount of armor (and therefore needing more hits to kill than other things) and also it being much less efficient than the blaze grinder for XP. I'll take a look at it, but I don't mind if you want to you do whatever with it.
Edit: Examined it. All the redstone machinery is still working as far as I can tell. All the switches are labelled, although some not obviously so. The master switch down the ladder in the observation lounge was off, which turned on all the lava pillars regardless of what the switches upstairs were doing. The switch small alcove in the back-right was also in "items" mode where all mobs are automatically killed and their items dropped into that water flow.
At least, that's how it used to work--apparently something has changed and either mobs don't drop anything when killed by lava, or the items get immediately destroyed. Other issues were spiders gumming up the works, creepers blowing stuff up, etc. In the end it was more trouble than it was worth and I just shelved the project.
All of the redstone machinery is still functional and accessible, if you want a tour at some point. Or, if you want to tour it on your own, I've flipped the master switch so it's working now. If you're not interested in keeping it as a historical project under whatever you're working on, I'll dismantle it and take all the redstone circuitry for re-use at a later date...
