Doi Castle (土肥城, doijo) is the ruins of mountain castle in Hakone mountain. This castle was placed at the top of Mt. Shiroyama which has 400m high. Sanehira Doi who is one of the warrior of Yoritomo Minamoto built this castle during 12th century. Because this castle was very important for battle, this castle was used until 16th century. Many ruins are still keep the original condition.
You can enjoy great view of Izu and Manazuru Peninsula. Nice mountain for hiking with history near by Hakone and Atami.
Tourist Info.
There is parking at the beginning of hiking course.
Access
0. at Kozu Station
1. use JR Tokaido to Yugahara (24 min.)
2. walk north west (1 hr.)
1 hr. 30 min
New Wave Samurai Movie. 
映画好き集まれ！ 
Nice Mountain for one day hiking. This is very old type of Japanese mountain castle. When you stand at the top of the castle you can see why this castle was very important. There are many gates which preserved well and tells how the castle was effectively built by the time.
Type of Castle: Mountain