Sheol

Sheol was the single inhabited planet orbiting the star Achshaph in the Ramshorn Spiral. Heaven was a city on Sheol. (PROSE: The Ruins of Heaven)

Behind the Scenes
Sheol (שאול) is the Hebrew word for the underworld. This is interesting, considering the city of Heaven, obviously based off of the land of the Afterlife, is contained within it.