
I found two videos of what it's like inside and a recording of a news broadcast of it. Most (pretty much all?) of the people in the mud in these videos are female.
https://www.youtube.com/watch?v=KIsQiJeKCHg
https://www.youtube.com/watch?v=e7yWe-A7448
https://www.youtube.com/watch?v=S4Berk3gBGE
Here's a link to the Bar's website in Japanese. http://gatabar.com