Trace of Koyama Castle

Koyama Castle was once a mighty mountain stronghold ruled by the Kimotsuki Clan. Its buildings were scattered around several man-made plateaus at the top of the mountain, rather than built on the tall stone foundations commonly seen on other Japanese castles. The defenders took advantage of the natural height of the landscape and cut deep ditches into a soft type of volcanic soil called shirasu to protect against intruders. The Kimotsuki Clan was based at Koyama Castle from the 12th to the 16th century, with its domain expanding to include the majority of Osumi Peninsula in the 1500s. Soon after it reached the height of its power under Kimotsuki Kanetsugu, however, the clan fell to the neighboring Shimazu Clan.

Although none of the structures remain standing today, a path winds through the mountain with signs marking the sites of different parts of the castle. Around the last week of November, the leaves of a giant gingko tree at the entrance turn a vibrant yellow.

Open to the public.