Inuyama Castle (Inuyama-jō) is located in the city of Inuyama, Aichi Prefecture, Japan. The castle overlooks the Kiso River, which serves as the border between Aichi and Gifu prefectures. Inuyama Castle is one of the 12 castles still in existence in Japan that were built before the Edo period.
Inuyama Castle is often claimed as the oldest castle in Japan, with original construction being done in 1440. According to Engishiki(a Heian Period-book), Harigane Shrine (a Shinto shrine) was moved to make way for the castle. That structure has been heavily augmented over time, and the current towers were completed in 1537, by Oda Nobuyasu, Oda Nobunaga's uncle. Though the antiquated architectural style of the watchtower atop the tenshu has in the past led many historians to believe this to be the oldest extant tenshu in Japan, that honor goes to Maruoka Castle, built in 1576. Construction on the main tenshu (donjon) at Inuyama began in 1601, and continued through 1620.
It was long believed that the donjon of Inuyama Castle was moved to the castle from Kanayama Castle in 1599, until such theory was disapproved as a result of examination through a large scale restoration work, involving the dismantling of the donjon, carried out between 1961 and 1965.
Entry into Inuyama Castle also allows visitors to enter into the Inuyama Artifacts Museum (Inuyama-shi Bunka Shiryō-kan) and the Karakuri Exhibition Room (Karakuri Tenjikan). Both of the exhibitions focus on cultural and historical artifacts of the city.
Source, Images: http://en.wikipedia.org/wiki/Inuyama_Castle