At Hasedera, there is a cave called Benten-Kutsu. Inside the cave, along the walls, are carvings of Benzaiten, the goddess of the sea, and her children.
It’s not a big cave by any means, nor is it deep. But it’s dark and damp, and quite low in places. Being at the far end of the temple complex, it’s easy to miss, but don’t! Make sure to explore right to the end—just watch your head!