Nanatsugama Caves (Genkai National Park)

Nanatsugama, meaning "seven caves," is a set of sea caverns carved into a basalt cliff face along the Genkai Sea coast near Yobuko, within Genkai National Park, formed over thousands of years by wave erosion acting on the columnar basalt rock. The caves vary in size, with the largest reportedly able to fit a small boat well inside its mouth, and their dark openings against the layered, hexagonal basalt columns are the main visual draw, best appreciated from the water rather than from land, since the cliffs are not easily accessible on foot. Sightseeing boats depart regularly from Yobuko Port and cruise along the base of the cliffs, entering several of the larger caves when sea conditions allow, with a full round trip taking about 40 minutes. The boats also pass close to the cliffs' dramatic rock formations and, depending on the route, may offer views back toward Yobuko Ohashi Bridge. Because the caves are exposed to open sea swells, calm-sea mornings give the smoothest ride and the best chance that the boat can safely enter the caves; rough weather can shorten the route or cancel entry into the caves altogether, so checking conditions before booking is worthwhile. The experience suits visitors comfortable on small boats, and life jackets are provided; spray from the sea is common, so waterproof layers are advisable even on calm days.