I had some excellent time in the onsens and took some pictures.
Here I am in the highest level onsen called a rotenburo. I had to hike for 25 kilometers before I found the natural and elusive rotenburo:
Also, here is a picture that my girlfriend took inside the ladies onsen up on Mt Winaki:
Finally, my girlfriend took a picture inside a waterfall-type of onsen near Niigata prefecture set deep in the Japanese Arupusu:
Nakedness is very common in Japan and people don't associate sex with nakedness as they do in the west. People are not ashamed of their bodies as they are in Western countries and this is part of the beauty of Japan.
Please notice that the woman with small breasts in the picture is wearing a ceremonial octopus on her head for bathing.