The Navel of the World (世界のへそ Sekai no heso) is the entrance to the Heavens. As the name implies, it is located in the very center of the world; the center of Sentora. It is a long garden-like pathway consisting of a large ivory tower that holds the Heaven’s Gate at its center. It is generally unfrequented by all surface dwellers, but as a safety precaution to prevent people from discovering the gate, hundreds of Themis Traps guard the pathway.
Despite hosting a "huge ivory tower", the tower itself is never actually seen.