Infinite Staircase
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The Infinite Staircase is an alternative means of planar travel if you don't mind getting a little exercise and aren't afraid of heights. The "base" of the stairs is in the palace of Argentil in the divine realm of Selune on Ysgard, and from there it goes up, well, infinitely. It starts out as a simple spiral staircase, but very quickly turns into something out of an MC Escher drawing. On almost every landing of the staircase is a portal leading to one of the planes.
The staircase connects to any plane where creativity is being expressed. In practice, this means any plane that has intelligent life, which is basically all of them. The staircase is maintained and guarded by lillendi.
The Infinite Staircase debuted simultaneously in the Planescape adventure "Tales from the Infinite Staircase" and the Forgotten Realms adventure "For Duty and Deity", and hasn't been heard from since.
Gallery
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The Nowhere Inn, a landing turned into an open market.
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Backwards long jumping is the most efficient way of traversing the staircase.