Unbuki Underground Seawater Cave
While many of the mysteries of the underwater limestone cave of Unbuki are slowly being revealed, the largest remains unsolved. While the entrance to the caves is about 400 meters inland, the saltwater inside is tidal, which indicates the presence of another entrance under the seabed. Despite ongoing exploration by expert teams, however, no connection has been found. Formed by the collapse of limestone bedrock, Unbuki is reminiscent of the famous cenotes of Mexico, sinkholes which connect underground water sources to the surface. In fact, Unbuki is an anchialine pool, a landlocked body of water connected to the ocean by an underground cavern.
Another World
The sizeable area around the entrance to the caves, itself a few meters below ground level, can be illuminated by switching on the lights at the site. Researchers from the National Institute of Technology, Sasebo College in Nagasaki Prefecture, ran experiments at Unbuki using remotely controlled robots and sonar technology to model the caves, publishing an academic paper on their findings in 2014.
Ancient Discovery
A team of expert divers led by renowned Japanese explorer Hirobe Toshiaki began surveying the site in September 2018, beginning with a dive to 300 meters. This initial exploration confirmed Unbuki as Japan’s longest underwater cave and discovered earthenware estimated to date from the Neolithic period.
Rare Creatures
The next series of dives uncovered what appears to be a new variety of shrimp, and the first footage shot in Japan of the unbuki-anago eel. The eel, which grows up to 50 centimeters long and is also known as Fryer’s false moray, is found in very few places in the world and was first identified in Japan at Unbuki in 2014. The team believes it is possible there are as yet unidentified creatures in this unusual habitat, including some that may not exist anywhere else on the planet.
Still Baffled
Divers who followed in the footsteps of the initial expedition have since traveled 700 meters from the entrance through the twisting and turning caves, a considerable portion of which must run under the seabed but were unable to locate the connection to open water.
Getting There
Unbuki is on the northwest coast of the island a few minutes’ drive or less than 10 minutes’ walk from the airport. There is free parking for a few cars. Admission to the site, accessible via steps directly from the parking lot, is free. Please note that while visitors are free to explore the entrance and its surroundings, diving in the caves is prohibited.
