The caves were formed specifically by the wave-driven erosion of columnar jointed basalt.
The name 'Nanatsugama' translates literally to 'Seven Cauldrons,' referencing the shape of the seven main sea-level openings.
The basalt cliffs here are geologically linked to the volcanic activity that shaped the Northern Kyushu region.
The largest cavern is large enough for small sightseeing vessels to enter during calm tide conditions.
The site is officially protected as a Japanese Natural Monument due to its unique geological morphology.
Nanatsugama consists of seven distinctive basalt sea caves formed by the erosion of volcanic rock along the Genkai Sea coastline. Located in Karatsu, Saga, these formations are designated as a National Natural Monument of Japan. The largest cave opening measures approximately 3 meters wide and stretches roughly 110 meters deep into the cliffside. The hexagonal basalt columns were created through the rapid cooling of lava flows. Visitors can view the caves from a clifftop observation deck or via sightseeing boats that enter the larger chambers when sea conditions permit. The surrounding area features a grassy park and walking trails that follow the cliff edge. These geological features are part of the Genkai Quasi-National Park. The site is accessible year-round, though boat operations are strictly dependent on wave height and maritime weather conditions.
The sightseeing boat provides the best perspective looking out from inside the main cave toward the open sea.
Check the daily marine weather report before traveling, as boat tours are often canceled due to high swells.
Bring binoculars if you plan to view the caves from the clifftop observatory to see the interior detail.
Wear sturdy, closed-toe walking shoes to navigate the unpaved paths around the cliff edges.
Do not attempt to climb down the cliffs; stay on designated trails to avoid hazardous, loose rock.
Boat tours may suspend operations during winter months or periods of high wind and rough seas.
Stay behind safety railings at the cliff edge and keep to marked paths to protect the surrounding flora.
