Most unusual dungeon deisgn that you saw in video games

[Ferocity]

What were the most unusual and interesting dungeon designs that you saw in video games?

For me it was:
1. South Shrine in Shining the Holy Ark. Some tunnels were having some kind of gravitational switch, so after passing through them, floor and ceiling switch places, which made it very confusing.
2. SkyTown maze in Dragon Warrior VII. Cubic maze which flips around as you reach the end of one side.
3. Demise: Rise of the Ku'tan. Sheer size. The most hardcore and convoluted dungeon ever made. People play for years to finish it. Not randomly generated.

[Duronos]

I may not be to well versed in many dungeons but Blackrock Depths from WoW always caught me as an unusual design along with Sunken Temple (old Sunken temple).

To go with a series I've played a bunch of which many of you know as Zelda, I'd say the Minish Cap has some interesting and unusual designs compared to most Zelda games such as the Sky Temple.

I'd have to search a bit more in my memory to see if I have any more unusual designs from other games that I've played as I don't feel like what I've said has sufficed.

[Val the Moofia Boss]

The Reverse World in Pokemon: Platinum was a pretty weird dungeon; surfing on walls or walking up side down, and the gravity was all over the place.

I can't remember the name of the game, but there was this massive dungeon that required you to run all over the place. Many of the bosses were locked until a certain objective was completed, so alot of time you found yourself running back and forth between places you already visited to cleave through new rooms. At one point, I had to run back to the entrance four times after completing four different objectives hours apart from each other just to access the librarian's room, which is right in front of the entrance. I probably spent twice as much gametime running around the dungeon then fighting in it. Kinda reminds me of Naxxramas, but at least there all of the paths are linear and bosses unlocked progressively, and teleporters bring you back to the center, so you don't waste time running around everywhere.

[Arkenaw]

The twisting tunnels in the Ocarina of Time's forest temple are still one of my favorite things ever.

[Chingylol]

Startropics for NES has some amazing dungeon design. An extremely underrated game that I haven't heard anyone ever mention, sadly.

I would go as far to say it was better then the original Legend of Zelda. Blasphemy, I know.