Tunnel Network

[Vlaid]

I've often thought that something the underdark is missing is some kind of maze-like tunnel network. So...

First create a very large maze-like area of crampt tunnels, with dozens of iterations. Connect about 5-6 of them together each time a reset happens so they feel truly randomized each reset. Fill them with a lot of weird thigns like little camps of roachmen, sections infested by beetles, cultmen who have swarms of rats at their command. Just a really weird creepy place.

Then you could do a few things....

-Tie pitfall traps in various areas into this tunnel network but with only certain areas you could exit with a rope and grapple (or far fewer areas you could exit by foot).
-Allow a random chance when digging a hole in certain areas to create a hole that can take you into this tunnel network (good for sneakily traveling around the underdark)
-The danger of these tunnels likely should not be too extreme but mostly an annoyance/chance for unique exploration/travel/different kinds of randoms.

Basically just a big maze of tunnels that changes every reset with many different connected modular areas of the tunnels that exists below a lot of areas of the underdark.