The Eternal Boundary is an adventure module for the 2nd edition of the Advanced Dungeons & Dragons fantasy role-playing game.

The Eternal Boundary, the first adventure for the Planescape setting, focuses on a few key areas of Sigil.

The player characters are hired to locate a madman who holds the key to a portal, and explore the slums of the Hive, meet the Bleak Cabal at the Gatehouse, and parley with undead in the vaults of the Mortuary.

[1] He suggests that when the player characters "can go anywhere in an infinite number of universes, it's hard to know where to begin.

[1] Swan concludes by saying: "Despite the reliance on familiar settings (a tavern, a mausoleum, a trap-filled citadel), the bizarre cast of characters and almost casual way that travelers flip between planes gives Eternal Boundary a feel all its own; you're unlikely to confuse it with a conventional fantasy adventure.