The Curse of Doors

The adventurers enter an ornate room with four doors, one they enter and the other three are closed. They also see a beautiful, valuable necklace lain on a table. A close examination of the necklace shows that there is writing in an ancient language on it. Knowledge of that ancient language shows that the writing is a number: 1d20+2.

Anyone who touches the necklace is afflicted with the curse of doors: opening a new door while wearing the necklace opens the door to infinite possibilities. A door may open to any room or room like area, in any place, plane, or universe. The only requirements are that the area immediately around the room is breathable and livable by humans and that there is at least one other door somewhere nearby.

If someone afflicted with the curse attempts to open a new door without the necklace, the door will open back to the room the necklace is in. If they attempt to leave the necklace in a different room the doors will open back up to that same room with the necklace. If one person carries the necklace away from others afflicted with the curse, the others will find that opening a new door will lead them to where the necklace is. Open doors will still connect back to rooms that have been visited, allowing connections as long as the doors remain open.

Someone not afflicted with the curse must be careful or they will be quickly separated from those that are afflicted with it. It may not be easy for the adventuring party to realize that before it is too late and you have forcibly split the party.

Once a new room is opened and entered, the number on the necklace decreases by one and the door just used can not be closed to open a new room. Closing the door and reopening it merely leads back to this same room. A new door must be found.

The implication, though it should not be stated, is that getting the number on the necklace to zero ends the curse. That is one possibility. 

You can do all sorts of cool things with this curse. You can foreshadow modules or adventures you want to run later where the cursed end up in a room from one of them and then they run into that same place later by reaching it normally. Use rooms from super weird modules that do not make complete sense in your setting. Have the players pop into the lair of a recurring villain or see some nefarious plot unfolding and then they leave without knowing where it is.

The rooms you use should be very gameable with a built in conflict preventing movement to a new door. The rooms, or areas of the rooms, should have interesting things to interact with. They should be immediately evocative to differentiate them from previous rooms they entered. Also, remember that the player's characters may be entering into situations that do not make much sense to the people and groups they are intruding upon.

I recommend checking out Labyrinth: the Adventure Game for a good technique and bunch of examples of doing this for room-like areas. Other touchpoints for the way this sort of procedurally generated curse could work or for more inspiration for rooms:

Depthcrawls like The Gardens of Ynn and The Stygian Library (maybe eventually my settings of the The Grand Bazaar and its denizens could be of some use in this)

Bluebeard's Bride RPG

Alice in Wonderland

Infinity Train

The Lost Room

Quantum Leap

Sliders

The Pagemaster

I originally had this idea when trying to come up with interesting and gameable curses for my OSR campaigns but I also kind of like it as its own system where the rules would be hyperminimalist and the real meat of the system would be just a ton of rooms I write as places the group has to visit and deal with and survive through. I have started work on that a bit here... because I always need more projects.