The Sea Serpent Cavern is located underground and it has two entrances, One near the Needlepoint Spire, the other is somewhere near the Mysterious Ruins, and is entered via the Serpent's Mouth. You can see this in Power Cruising and Island Flyover.
Island Flyover Information:
- Daytime: “This twisting sea cave snakes underneath the Mysterious Ruins.”
- Evening: “This spooky sea cave is now a playground for Power Cruisers.”
- Night: “At night, the cave has a kind of calm, tranquil atmosphere."
During nighttime in Island Flyover, you can hear some singing coming from the cave.