This weekend I did a little sightseeing around where I'm staying, in Kawaguchiko, Japan. There are a series of caves you can visit at the foot of Mt Fuji, formed from lava from the last eruption. The Narusawa Ice Cave is one of them, and is a National Monument. And also a little bit scary to get through due to the extremely low ceilings. 
The entrance is fascinating, as you go down under the floor of the forest, and suddenly it's literally ice cold, like you've walked into a fridge. The haze you can see in the photo is the air condensating between hot + humid and freezing!
A walk in the sea of trees, along lava strewn paths, was also truly beautiful: it had my favourite combo of moss and ferns.
I visited a site called Saiko Iyashi no sato NENBA, a recreation of a thatched village that was destroyed by a typhoon in the 60s. Each lovely building had examples of local crafts.
And of course, a visit to the opposite side of Lake Kawaguchiko, to get a magnificent view of the sacred mountain, looking just like a Hokusai print.