足柄城, Ancient castle ruins in Kanagawa Prefecture, Japan.

Ashigara Castle is a mountain castle (yamajiro) on the Ashigara Pass, on the border between Oyama in Shizuoka Prefecture and Minamiashigara in Kanagawa Prefecture. Its honmaru and five main kuruwa, plus smaller enclosures and dry moats (horikiri), remain on the ridge. A 2009 excavation uncovered a large vertical moat (tatebori); a roughly 600-metre walking path runs through the main enclosure.

The castle was built during Japan's feudal period as a strategic military fortification to control mountain passes between Kanagawa and Shizuoka regions. It served as a key defensive position in this mountainous frontier area.

The ruins display traditional Japanese fortification methods with stone walls built according to period construction principles. You can see how builders adapted the defensive structures to work with the steep mountain landscape.

Visitors can reach the ruins by following marked hiking trails that wind through forested slopes with informational signs about the archaeological features. The uneven terrain requires good footwear and careful attention when exploring the different sections.

The stone structures show the engineering skill of medieval Japanese builders who designed their fortress specifically for steep mountain terrain. This adaptation to the landscape sets this site apart from flatter fortifications found in other regions.