Weird Dungeon Geometries

Troll and Flame has had a couple of posts discussing Geomorph Cube Dungeons, which reminded me of my favorite weird dungeon geometry: a Möbius Loop.
I believe this came from Dungeon magazine issue #26 (or thereabouts). At some point in the adventure, the party entered a corridor that was a Möbius loop. (I’m guessing the party was on another plane or somehow gravity was changed so the party would always have their feet on the loop.)
You could probably do a whole dungeon in the same way, but only in one dimension. (Joining the top and bottom edges of the map or the left and right.) Draw a map on two sides of the paper. Make a loop and twist it as you attach it together. Make sure the corridors, walls, and doors match up on both sides of the paper where the edges meet when you join it together.
What other weird dungeon designs have you come across?
(By the way, I’m revising the stylesheet of the website, so bear with me.)
Higher-dimensional weirdness – walk down a corridor, and you find yourself back out towards the entrance, only you’ve been flipped, mirror-style. The party don’t realise, of course, unless they left someone outside – after all, the wizard’s spellbook looks the same to them, it’s every other source of writing that’s wrong!
…and then the chemist or biologist player gets a little too worried and demands that they flip themselves back right now, before they run out of food. Chirality’s a pain, y’know.
I came across a 1-Page-Dungeon created by http://www.thealexandrian.net that had so much weird geometry. There were Escher stairs that only went up, corridors that crossed over each other in two dimensions while being arrow-straight, and best of all, a set of Möbius rooms–there were 8 rooms arrayed in a 3×3 square. You went through each room to the next, and once you’d gone through the last door in Room 8, you emerged onto the ceiling in Room 1, and had to right around again to find the door back to the rest of the dungeon.