That a natural phenomenon or an object like a mountain, a rock, a spring, or waterfall could be sacred or home to something sacred is not at all uniquely Japanese, but a fairly universal occurance. However such things are commonly found throughout Japan. This is Oyama Shrine in the mountains of Dogo, the largest of the Oki Islands that are part of Shimane.
There is a torii and a couple of lanterns, but no buildings. The shrine is a giant tree. It is a sugi, commonly called Japanese Cedar but it is not actually a cedar. It is estimated to be over 800 years old.
In April villagers from Fuso, a fishing village on the coast at the base of the mountains, come here with a long vine and wrap it around the base of the tree seven and a half times. I am unsure if there is a significance to that number. Ritual objects that carry prayers and requests are then inserted into the wrapped vine.
There are quite a few sacred trees on Dogo, a nearby one being the Chichi Sugi. Being remote and isolated the Oki Islands have kept a lot of traditions.
To get a sense of the size of the tree you could see the cover photo on my facebook page