The Spire

The Spire is a mysterious structure that sits at the center of the Outlands. Looking up from the ground, it does not appear to have a top, though in the distance one can see the torus that contains within it the city of Sigil. The Spire's true nature is unknown, as it appears to everyone as something different -- a mountain, a tree, perhaps even a living creature such as a serpent.

There is also some very powerful force related to The Spire, because the closer one comes to it, the fewer things work. Spells fizzle, fire won't burn, even chemical reactions don't occur as they should. Even the powers of the gods themselves don't work if they come too close. What causes this is unknown, but it does have its advantages. Note that this does not apply within Sigil, which is safe from all of these effects.