Explore the deeps of Japanese countryside
There are a surprising amount of caves in Hokubo, so if adventure is the purpose of your trip you won't be disappointed.
If you are going to Kanba waterfall this cave is just on top of the entrance. Also known as Oni no ana. On a steep climbing of a 10 minute walk at a constant phase. Well lighted and deep cave with wide and high pathway.
At the end of the way that is about 2 minutes far you'll find some kind of offering table.