For all of you dungeon-lovers: Which dungeon do you think is comparable to Durlag's Tower in BG? Honestly I believe the undermountain is the only possible candidate . DT is very unique as it has a good background story and have very well written lines in the game (I mean, those books). The whole dungeon is very immersing (not like Watcher's tower as there is no link between two levels).
Actually, I have always been thinking about making a mod for NWN, using the "ice island" idea from ToSC. Say, the island is a creation by the mad God Cyric as a symbol of avenge to the Goddess of magic. And you, the player, are sent by your master to investigate the island. You will meet, say, a Paladin of Kelemvor (also a foe of Cyric), and you two will dive deeper into the ice prison and somehow destroy the mechanism that forbids all magic users to teleport. I'm considering 3~4 levels with each level full of puzzle as well as secret passages; 5-6 hours of playing, which is essentially, a vast dungeon, yet a small and manageable mod.