Parvus

Parvus is a rocky world riddled with caves. Its native life forms such as the Galax all live underground, but unfortunately Parvus is also prone to quakes, which make the caves unstable.

"The Big, Small Rescue"
When quakes threatened to wipe out the Galax, Boulder took the Rescue Bot recruits to the planet via the space bridge. They were able to retrieve the Galax, despite multiple cave ins, and return to the space bridge.