These are the Hashigui-iwa Rocks, a natural monument in Kushimotocho, Wakayama Prefecture.
Long ago, Kobo Daishi and an amanojaku made a bet over whether they could build a bridge from Kushimoto to an offshore island before the rooster crowed. Just as Kobo Daishi had nearly finished setting the bridge’s piles, the amanojaku feared losing, imitated a rooster, and tricked Kobo Daishi into thinking morning had come. Kobo Daishi gave up and left the partly built bridge behind. That is why only the bridge’s piles are said to remain, according to the legend.

What do you suppose Kobo Daishi and the amanojaku wagered?

These Hashigui-iwa Rocks are also selected as one of Japan’s Top 100 Sunrises.