Onigajo is a spectacular coastal landscape in Kumano City, Mie Prefecture, designated as both a Place of Scenic Beauty and a Natural Monument of Japan. Along the rugged coastline facing the Pacific Ocean’s Kumano Sea, countless sea caves and unusual rock formations have been carved by powerful waves and shaped by geological uplift. Stretching approximately 1.2 kilometers, these dramatic formations resemble a series of natural sculptures created by the forces of nature.
The caves and rocky ledges are arranged in a staircase-like formation, a result of the combined effects of coastal erosion and land uplift caused by earthquakes. Onigajo lies at the southern end of the ria coastline extending from the Shima Peninsula. Farther south, the rugged cliffs give way to the gently sloping pebble beach of Shichiri Mihama.
Onigajo was designated a National Natural Monument in 1935. In 1958, nearby Shishiiwa, or Lion Rock, was added to the designation, and the area became known collectively as Onigajo and Shishiiwa in Kumano, recognized as both a Place of Scenic Beauty and a Natural Monument. The site is also part of the UNESCO World Heritage property Sacred Sites and Pilgrimage Routes in the Kii Mountain Range, inscribed in 2004, and is included among Japan’s 100 Scenic Landscapes.
At the top of the mountain are the remains of Onigajo Castle, reportedly built around 1523 by Arima Tadachika as a retirement stronghold during the Muromachi period. The castle was later conquered by the Horiuchi clan, who served Toyotomi Hideyoshi and governed the area until the Battle of Sekigahara in 1600.
A hiking trail connects the summit with Matsumoto Pass, part of the historic Kumano Kodo pilgrimage routes. Along the trail, visitors can still see three surviving karabori, or dry moats, which were defensive features of the former castle.
A hiking trail runs from Onigajo’s eastern entrance toward the summit, passing through areas planted with cherry trees. In spring, four varieties of cherry blossoms flower in succession, extending the viewing season and creating an attractive setting for a leisurely walk.
At the summit, a viewpoint known as Oni no Miharashidai, or the Demon’s Lookout, offers sweeping views of the Kumano Sea. The combination of rugged coastal scenery, mountain trails, and seasonal blossoms makes Onigajo appealing to both nature lovers and hikers.
According to local legend, the warrior Sakanoue no Tamuramaro was ordered by Emperor Kanmu to defeat a notorious pirate named Tagamaru, who terrorized the region and was feared as a demon. The story is one of the traditions associated with the name Onigajo, which can be translated as “Demon’s Castle,” and adds a layer of folklore to this dramatic coastal landscape.