The Great Bounce

The Great Bounce is a massive geographical feature of Poorthwart, located in the Southeast corner of the land. It is believed that significant regions exist beyond it, but these are unknown.

Purpose
The Great Bounce is a mechanism that is used by the Sun and the Moon to launch themselves back into the top of Poorthwart following their long trips from North to South. This is necessary because Poorthwart is not round/globe-shaped, but rather exists in a top-to-bottom plane.