This is a crater of the Mt. Kusatsu Shirane(2160m 7087ft) in Gunma Prefecture. It is named Yugama in this mountain.
There is a big parking lot, and it will be possible to go there in about ten minutes. It cannot enter other places because of the hydrogen sulfide gas.
Here is not a climbing mountain but a sightseeing spot. The tourist of the overflow from the parking lot if becoming holiday visits.
There is Mt. Hon-shirane on the opposite side of the parking lot.