The gorge is deep, and the depth is the first thing you feel.

Aso erupted twice—once about 120,000 years ago and again about 90,000 years ago—and each time the pyroclastic flow ran down and cooled and hardened here. The Gokase River has been cutting through it ever since. Walk the path along the canyon and the rock beneath your feet belongs to the older eruption while the rock above your head belongs to the younger one, thirty thousand years folded into the height of a cliff.

As the flows cooled they cracked into hexagonal columns—the formation geologists call columnar jointing—so the walls rise in vertical flutes, as though the stone had been combed. They reach a hundred meters at the highest point and run seven kilometers east to west. The whole canyon is a designated national scenic beauty and natural monument.

Manai Falls drops seventeen meters from the rim, and in autumn the trees around it color and frame the white of the water. You can take a rowboat to the base and look up: red leaves, falling water, and a long narrow seam of sky. The only sound is the water.

The walking path runs about a kilometer. Boats must be reserved online in advance, and autumn weekends fill early; the quietest hour is the morning, when the light first reaches the bottom of the gorge.

This is also where the grandson of the sun goddess is said to have descended to earth. Standing at the base of the cliffs, with the sky closed to a ribbon overhead, you understand the choice of setting. If a god were going to come down anywhere, it would be somewhere this deep, and this quiet.