I really like Frostholm. The story is fun, and it's not endless like some dungeons can be. I also like . . . Vault of Ice, Shirataki Temple, Ironworks, and Grand Chasm Past was interesting.
Big Ben remains my favorite. I love the old England flavor of MB but beyond that it's also a hoot. I just love spilling the milk and getting that big old cat to cry over it.
Malistaire, of course. You can't beat the story leading up to the final battle with him. The cut scenes are my favorite. Another wizard and I visit his lair as often as possible. We might be Archmages, but we still enjoy fighting EVERYTHING in the dungeon until we face Malistaire.
We taunt, torment, and grovel, then we bring cookies, cakes and pies to bribe Malistaire with. We make the dungeon more challenging by stripping down to noob gear (no wands, no amulets, no athames, no clothing boosts, no rings). The only thing you could keep is your pet. That sure makes it more challenging!
Yep, Malistaire's lair is my favourite, too. I like dark stuff, am evil, and quite enjoy wreaking havoc up there in my noob gear. ;)
QueQueg and I have led quite a few noob fights, during which we and our friends make our way through the entire dungeon without any gear on. We grovel, we taunt, and probably offend everything within 5 miles of us. :D
BTW, that cut-scene is totally ruined~ I'll never think of it the same way again! :P
