Mount Horaiji

Mt. Hōraiji: A Volcanic Sacred Peak in Okumikawa

The first thing visitors notice on the climb to Mt. Hōraiji is the rock itself. Black, glassy shōshigan—pitchstone—appears on the cliff faces and in the steps underfoot, a volcanic glass so unusual that the Geological Society of Japan chose it in 2016 as the prefectural rock of Aichi. The mountain that produces it rises 695 metres above the Okumikawa highlands in Shinshiro City, the eroded remains of a rhyolitic volcano last active some fifteen million years ago.

In July 1931 the whole mountain received a dual designation, as both a Place of Scenic Beauty and a Natural Monument. The two categories rarely overlap on a single site, and the citation lists six separate criteria for inclusion—from rock structure and panoramic views to the wildlife and rare epiphytes that cover the cliffs.

A path of 1,425 stone steps

The mountain takes its name from Hōrai-ji, the Shingon temple on its eastern flank. Tradition holds that a hermit named Rishu founded the temple in 703, after curing Emperor Monmu of illness through seventeen days of esoteric prayer. The name Hōrai derives from a legend in which Rishu rode a phoenix (hōō) to the imperial capital; the mountain itself was earlier known as Kiriu or Enganzan.

The approach is famous in itself. From the base car park, a flight of 1,425 stone steps passes under the Niō-mon gate, climbs through cedar groves to the temple's main hall, and continues to the Oku-no-in viewpoint near the summit. Many of the steps are cut from the very rocks the mountain is made of—visitors who look closely can pick out the lighter rhyolite from the darker, lustrous pitchstone underfoot.

About a third of the way up stands the Kasasugi, a giant sugi cedar of around 800 years. It is 60.8 metres tall and named for the parasol-like spread of its upper branches; it is one of the trees on the New Hundred Famous Trees of Japan list.

The Tokugawa connection

Rishu's temple drew imperial and warrior patronage from early on. Minamoto no Yoritomo is said to have rebuilt it in the Kamakura period; later legends place Takeda Shingen here during his ill-fated final campaign, and the young Ii Naomasa is said to have taken refuge on the mountain as a child.

Its decisive moment came in 1648, when the third shogun Tokugawa Iemitsu, on a pilgrimage to Nikkō, read the Tōshōsha Engi and learned that his grandfather Ieyasu had been born after his parents prayed for an heir at Hōrai-ji's image of Yakushi, the Buddha of Healing. Iemitsu resolved to enshrine Ieyasu on the mountain itself. The Hōraisan Tōshōgū was completed in 1651, the same year as the present Niō-mon at the foot of the stone steps. Both are designated Important Cultural Properties, and the shrine is counted, with those at Nikkō and Kunōzan, as one of the three great Tōshōgū of Japan.

Rocks, cliffs, and a famous misidentified bird

The geological reasoning behind the 1931 designation is detailed. The mountain's rhyolite shows pronounced flow banding, and parts of it have transformed into glassy pitchstone in which a fine "pearlite" structure has developed—a combination, the citation observes, with few parallels elsewhere in Japan. The Mirror Rock (Kagami-iwa), the largest single cliff on the mountain, is itself composed mainly of pitchstone. Hōraiji-san has been selected as one of Japan's One Hundred Geological Sites.

The cliffs run for several kilometres along the upper ridge. Tengu-iwa to the north and Gorō-iwa to the east are equally sheer; the Gyōja-goe traverse, used in earlier centuries by yamabushi mountain ascetics, is the most demanding stretch. From the rocks above Oku-no-in the view extends south across the Mikawa–Enshū plain to the Atsumi Peninsula and the Pacific.

The wildlife is the other half of the designation. The Konohazuku, or Japanese Scops Owl, is a small brown nocturnal bird whose three-syllable call—buppō-sō, buppō-sō—was heard by earlier generations as the Three Treasures of Buddhism: Buddha, Dharma, Sangha. For centuries the call was attributed to a different, more colourful bird (Eurystomus orientalis) which carried the same name. The confusion was finally resolved in June 1935, when NHK Nagoya broadcast the call live from Hōraiji-san. A listener in Yamanashi tracked the sound to its source and discovered, to general astonishment, that it was the owl. The Konohazuku is now both the Aichi prefectural bird and the city bird of Shinshiro—though, sadly, its call has become rare on the mountain since the construction of the Skyline parkway.

What to look for on the way up

The Niō-mon gate, completed in 1651 by the Hamamatsu master carpenter Yamazaki Shichirōbei, is a three-bay, single-doorway gatehouse with a copper-sheet roof (originally cypress bark). The deep eave brackets carry painted carvings of bamboo and tiger, peony and lion, rhinoceros on waves, and a kirin in clouds. The temple-name plaque above the doorway is a copy of one tradition attributes to Empress Kōmyō, painted as thanks for the recovery of Emperor Shōmu after prayers to Hōrai-ji's Yakushi.

Vegetation shifts noticeably with altitude. Lower slopes carry a mixed forest of evergreen and deciduous broadleaves, with warm-temperate species at lower elevations and rocky outcrops thick with ferns and herbaceous plants. Near the ridge the conifers take over and the air grows cooler. Vertical cliff faces support colonies of rock tripe (iwatake) and other lithophytes, one of the criteria the 1931 designation specifically mentions.

Around the mountain

The Hōraiji-san Museum of Natural History at the base of the climb has detailed displays on the mountain's rocks, fossils, plants and animals—a useful first stop for visitors who want to recognise pitchstone before they walk on it. The neighbouring Yuya Onsen, on the Itashiki River in the Hōraikyō gorge, is a hot-spring resort with roots in the same Rishu legend, and the Atera-no-Nanataki, themselves a national Place of Scenic Beauty and Natural Monument, are within easy driving range.

For visitors who prefer not to climb the full 1,425 steps, the Hōraiji-san Skyline parkway reaches a car park near the upper temple, from which the Niō-mon, the main hall, and the Tōshōgū are all within a short walk. Autumn maples on the upper slopes draw the heaviest visitor traffic from late November into early December.