Takachihokyo, Natural gorge in Takachiho, Japan.

Takachihokyo is a V-shaped gorge on the Gokase River, about 25 km southeast of Mount Aso. Its near-vertical walls, averaging 80 m and reaching 100 m, are made of welded Aso pyroclastic-flow deposits with columnar jointing, resting on Chichibu slate and sandstone. The gorge runs 7 km east-west, and Manai Falls drops 17 m into the river.

The gorge was formed when pyroclastic flows from Mount Aso, erupted about 120,000 years ago, cooled and welded into andesite with columnar joints; the Gokase River then cut a V-shaped valley through it. A younger flow, from about 90,000 years ago, caps the upper walkway. In 1934 it was designated a Place of Scenic Beauty and Natural Monument as the Gokase River Gorge, and in 1965 it became part of the Sobo-Katamuki Quasi-National Park.

Manai Falls, at the centre of the gorge, is tied to the deity Amenomurakumo-no-Mikoto, who according to myth moved a water source here when the land had none during the descent of the heavenly grandchild; the spring became the Tennen Manai and now falls 17 m. The gorge and its falls are among Japan's Top 100 Waterfalls, and from mid-July to mid-September the falls are lit until 10 p.m.

The 1 km promenade along the gorge links Manai Falls, the Sennin no Byobu rock and the Yaritobi Bridge, continuing to Takachiho Shrine; the stretch from the bridge is a stepped mountain path, so wear walking shoes. The promenade fully reopened on 1 March 2024 after Typhoon No. 14 closed part of it in 2022. Rental boats reach close to the 17 m Manai Falls.

The cliffs are made of welded Aso pyroclastic-flow deposits, not basalt: an older unit about 120,000 years old forms the lower gorge, and a roughly 90,000-year-old flow lies above the walking path. The two are welded together, and the columnar joints cut through this rock.