Gespenwald

Gespenwald is a freeform adventure set in a ghostly forest sustained by undead mycelium. The forest materialises for only one night per year, and players must explore it before dawn and avoid becoming stuck there.

Gespenwald is written for the Cairn TTRPG, but can easily be played with Into the Odd or any of its derivatives, adapted for other OSR games, or, like my previous publication Mostly Harmless Meetings, read simply as a piece of imaginative Oulipian fiction, if that's more your bag.