Inspired by misreading the name of a Christmas carol at a quick glance. The brain's ability to swap in a pattern until it sees what is really there means you get this lovely magic item.
Deck of Halls
The deck of halls is a 12-card deck of cards roughly four inches by six. Each card depicts a different dungeon corridor in a dungeon - usually far-flung dungeons or ones especially difficult to get to. Scrying magic (or careful research) may determine where those cards go.
The cards may be cut, shuffled, and otherwise handled and examined without activating them. To use a card, one must be drawn purposefully from the deck. Once drawn that card must be used or discarded before another card can be drawn. Once drawn, the card becomes a one-way portal (lasting one minute) to the corridor depicted on the card. Merely touching a card is enough to draw a subject into the depicted location. When a card is used or discarded, its magic fades and becomes just a simple parchment playing card. Each card may only be used once. Great for jumping from danger into new danger!
(GURPS): $1,000 per card remaining in the deck. Otherwise functions like a normal gate, except the size of the gate does not matter for drawing a subject in. Gates are one-way.
(Swords & Wizardry/retro-clone compatible): 1,000 gp sale value per card remaining in the deck. Any class may use the deck.
(D&D): 1,000 gp sale value per card remaining in the deck. Does not require attunement.
I imagine these cards depict a mix of very plain dungeon corridors that could be anywhere and much more specific ones. For example, ones decorated with heiroglyphs that lead to some lost Egyptian-themed tomb, ones covered with vines in the depths of a steamy jungle guarded by Aztec-themed orcs, holly-decked halls that lead to a festive land of elves, arched-roofed dungeons that echo with the stomps of the Lord of Spite, etc. A great way, at least potentially, to have PCs go to new dungeons. And if the big bad guy flees by throwing down a card to a strange corridor and runs through, do you let him escape with the gold and the McGuffin or do you jump in after him? 60, 59, 58, 57 . . . the GM's watch is counting down the seconds to decide . . . Merry Christmas, delvers!