'Xipiteckatic: The World of Rooms', Simon Silver, GURPS 4th Edition: Sarah Silver, Richard A. Silver, Marcus Carpathian, and Fujiwara Madoka.

We were sitting around a large circular table, ready to begin creation of my latest world, my sister, my dad, this guy I had been friends with briefly in college, and a Japanese chick who was here to brush up on her English, mostly just a warm body to fill our fourth required slot in order to properly catalyze the world, but useful as a greater wildcard than most. This game was a big test for me, I was stepping into some relatively unplumbed territory for me, both by using GURPS as the system, and not giving people much in the way of established guidelines for character creation, we were just going to wing it...

"So what's this mysterious world like bro? You've played this one a lot closer to the vest than usual, just system, point totals, and a few limitations and guidelines on character options..." My sister Sarah asked, and I began to explain.

Picture an old Victorian mansion: three stories plus attics and basement, a grand entryway that spans all three stories with balconies all around it and 'flying' curved staircases that connect them, with hallways that have only open door frames hung with beaded curtains instead of doors except onto the servant's staircases that go to attic and basement.

Now imagine that this mansion, instead of being surrounded by fields and grounds, is a tiny bubble of euclidean space inside a labyrinthine maze of rooms that connect to each other in an unstable and non-euclidean fashion: each one a bubble of stable reality in the midst of a sea of chaotic dark energy.

Now when I say 'unstable' what I mean is this: in this universe doors are portals between the stable pockets of the universe: and they don't always go to the same place when you open them. This is why the mansion has no doors, just beaded curtains, because it is a stable pocket where a colony of people live.

How do they survive without and outside to grow food you ask? That's simple: this and the other colonies like it eat packaged food they find in the basements and attics of the world.

You see when the doors of a colony connect to new rooms those rooms are not always bare, in fact rarely so, they typically are full of piles of junk, and sometimes other things: things like animate skeletons, Lovecraftian horrors, live Tigers, zombies, and so forth: things that will attack you. Midst the piles of junk in some rooms is edible food, typically canned but also sometimes in plugged in and running refrigerators and freezers with 'fresh' food, and this is what people eat. The faucets also almost always have running potable water so the 'colonies' rarely go thirsty unless the taps start running 'soft' with salt water, which can last for an hour, a day, a week, or longer, which sometimes leads to a colony being abandoned if it goes on too long.

The things in the colonies and the rooms come from a late TL7/early TL8 society, though occasionally things from earlier and later TLs appear, more 'earlier' than 'later', but there HAVE been lucky finds of things like **** swords, androids, pocket complexity 10 computers, and other high TL items.

Now you may be wondering how new colonies form and expand: that happens with 'Keys' and 'Windows'.