Tatami-ishi

Waves have planed the tops of these columns flat, leaving pentagons and hexagons about 1 to 1.5 m across that look like tatami mats laid on the shore, which gives the place its name. The Agency for Cultural Affairs counts several thousand of them and dates the lava to the Pliocene, and the tourism association gives about 6 million years. The town also calls them kikko-ishi, turtle-shell stones. The national designation came on 29 July 2014, and Kumejima Town owns the site.

Check the tide before you go, because the pavement shows best when the water drops. The Kumejima Sea Turtle Museum and Ou-jima Beach sit a few minutes away.