Unbuki Underground Seawater Cave

About 400 meters from the coast, the entrance to this underwater limestone cave drops into a saltwater pool whose tidal behavior indicates a second opening somewhere under the seabed, one that divers have yet to find despite reaching 700 meters into the passages. Formed by a collapse of limestone bedrock, the cave is an anchialine pool, landlocked but connected to the ocean underground. Surveys begun in 2018 confirmed it as Japan's longest underwater cave and turned up earthenware from the Neolithic period. Unusual marine life has been found inside, including a new variety of shrimp and the rare Fryer's false moray eel. Visitors can explore the entrance and surroundings; diving in the cave is prohibited.