If we pop one up it shouldn't be a problem. I'd like to keep a quest like that in, if possible. I'd set up the spawn area to be safe, put in a /kit to give each person the appropriate starter items, and set the area to not allow any changes out to a hundred blocks. Two options after that. The first is just to set up a number of lighted tunnels running off into caves. The one we are looking into is modifying a plugin we use on other servers that teleports a player to a random location. Hoping to do it so you don't appear inside solid rock Each player would appear somewhere up to 10k away from spawn, in their own area. We have pretty active admin/mods, about a dozen of us, so griefing is taken care of and offenders tossed out.
Arm twisting has been initiated.
That's nice, but none of the suggestions you're giving stop someone who finds someone else's base from deciding to create a dungeon smack in the middle of it.
And I admit I'm curious about your activity, this isn't the first time someone has posted to this thread about logging into that server and being immediately in a deathtrap.