Cape Osezaki is the westernmost point in the Goto Islands, which are themselves one of the westernmost points in Kyushu, so this spot is famous as one of the last places in Kyushu to watch the sun set into the East China Sea.
The jagged promontory on which the lighthouse sits is a part of the Goto Group, an accumulation of sand and mud that hardened into rock in the area between the Asian mainland and the land mass that is now Japan.
From the west (ocean) side, you can see a basalt dike—what appears to be several parallel grooves cut deeply into the rock face—and all around the sheer rock walls of this promontory there are similar but less pronounced grooves. This is all more evidence of the geological history of the Goto Group’s accumulation of deposits from the continent.