Yamanaka Castle was built by the Gohojo clan, who had their main castle in Odawara, between the Tenbun era and the Eiroku era (around 1530-1560) at the end of the Sengoku period. After that, Hojo Ujimasa, who was on bad terms with Toyotomi Hideyoshi in 1844, prepared for Hideyoshi's attack on Odawara, and hurriedly improved and expanded the moat and Daisaki Demaru.

Yamanaka Castle was counted as one of Hakone's ten castles and served as an important base for the Gohojo clan. However, in 1590, when Toyotomi Hideyoshi attacked Odawara, the castle fell in just one day.

The remains of Yamanaka Castle include a moat, earthworks, stone walls, and a demaru, which clearly retain the appearance of a mountain castle during the Sengoku period. The Yamanaka Castle Ruins Park also has castle models and an exhibition room introducing the history of Yamanaka Castle.