The Cavern Seas is a large and deep sea located in The 99 Caverns.
Though usually associated with Undertow Cavern, the Cavern Sea is a large body of water that is seen dividing two landmasses and is known for being one of the deepest regions in the 99 Caverns, thus making it a host to one of Dr. Blakk's Dark Water rigs at one point.
- Undertow (First appearance)
- Deep Water, Dark Water
- Mission: Improbable
- Back to Blakk
- Bandoleer of Brothers
- Dark as Night (Cameo, flashback)
- Slugterra: Return of the Elementals