One question Redrobes, why would the creator of the skull lair leave no exit/entrance to the outside? Sure he was probably a big, bad, evil guy up to no good, but I would assume (being a paranoid, evil, secretive wizard) his lair was warded against scrying and teleportation from the outside and it would easier for him to have a trapped/ guarded entrance for his minions and flunkeys to come through than leave a hole in his magic defenses. Its another kind of vulnerability in his defenses to be sure, but the lair is in a remote place and the creator would likely have some kind of nasty debuff/trap at the entrance.

Also, although you'll be doing 3d maps for the levels, I'd appreciate it if you could provide 2d overhead renders if you chose. I guess I'm hopelessly oldschool in my map preferences, but I have a future vile necromancer villain for my pcs in mind engaged in Things Man Was Not Meant to Know who would find a skull lair highly useful....

Keep it up, your lair is shaping up to be an evocative and memorable location....