The Chum Caverns are a group of caves that are underground between the Chum Bucket, and the Krusty Krab. They are seen in the episode "Chum Caverns". Plankton and Karen found them in an attempt to get to the Krusty Krab. Plankton and Karen stayed because of the beautiful scenery the Chum Caverns had. Customers go down to the Chum Caverns via a bucket shaped elevator.
The Chum Caverns are gorgeous caves. Next to them, there's a stream. Plankton was able to lure customers in because of how beautiful the caves were.
The Chum Caverns are inhabited by strange orange creatures known as the Cave Dwellers. Plankton found them and made them his slaves. Later, at the end of the Episode, The Caverns get destroyed and the Krusty Krab falls into the Cavern trapping everyone inside the restaurant and then Plankton ended up working for the Dwellers.