It is located 2 and half hours from Tokyo Metro. It is in Mt. Ogaku. It is the calcareous cave with many interesting stones.
Takes: 20 to 30 minutes.
Ogaku Cavern (大岳鍾乳洞) is a cavern located in Yozawa Valley. It has over 300m long. It is one of the major cavern in Tokyo. It was found in 1962. If you are big fun of spelaeanking, this cavern has lots to offer.
Tourist Info.
Admission: 500 yen
Close at: the Sunset.
There is a parking.
Access
0. at Itsukaichi Station
1. use Bas to Yozwa (35 min.)
2. walk west (25 min.)
500 JPY
30 min
Let's learn MJER Iaijutsu. 
映画好き集まれ！ 
It is located 2 and half hours from Tokyo Metro. It is in Mt. Ogaku. It is the calcareous cave with many interesting stones.
Takes: 20 to 30 minutes.