From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Pirate Cave (海底 洞窟, Kaitei Dōkutsu) is a cave located underwater.
The Pirate Cave was once the secret base of a Pirate Gang. The entrance to the harbor was a hallway covered with holes on the walls and buttons on the floor. If anyone touched one of the buttons, arrows would be shot from the walls.
Pirate Cave appeared in Dragon Ball: Daimaō Fukkatsu.
Pirate Cave is the eighth level in Dragon Ball: Advanced Adventure.
One of the ancient ships resembles a WWII-era submarine. On that note, one of the guns that the pirates purportedly owned resembles the Vz. 61 "Skorpion".