The seven caves of Nanatsugama can only be explored by a cruise leaving from Yobuko port. The columnar jointed caves are the result of centuries of erosion by the waves of the Genkai Sea. On a fine day, the black basalt rock of the caves contrasts with the bright green grassy plateau at the top of the cliff. At high tide, the boat can venture into one of the caves for about 50m beneath a vault 3m high - a grandiose sight!