Dungeon Descent is a rare Land card from Adventures in the Forgotten Realms (AFR), collector number 255. Current market price: $0.28 (foil $0.35), TCGplayer market prices via Scryfall.
This land enters tapped. {T}: Add {C}. {4}, {T}, Tap an untapped legendary creature you control: Venture into the dungeon. Activate only as a sorcery. (Enter the first room or advance to the next room.)