Legends of Dios
Geography in the underdark is on three axis. However travel is normally along known routes and tunnels. As tunnels close off and new ones open there are always new routes for the adventurous.
Up, Down, Notewise, Borkish, Dwardish, Rockwards
Notales is Notewise and up.
Borkales is Borkish and middle
Dwarven clans are Dwardish.
Dios is middle/dwardish.
Maine is middle/notewise/rockwards
Cedicea is upwards/rockwards/borkish
Drow are down (somewhere)
Shebog is rumored to be down (somewhere)
Styx is rumored to be down (somewhere)
Travel rockwards is extremely difficult as the terrain is hard, few tunnels exist and there are few scavengeable supplies. Travel downwards is difficult as few downward sloping channels exist. There are a few chasms but these are not easy as easy to travail.
Locales of Note
Crystal light caverns
Dagger rock tunnels
Deathbloom crevice, also known as pleasant death forest.
Fickle thorn forest