steven lim
Google
We  came here while on a visit to the Hells of Beppu. We had wanted one of the outdoor private onsens, but it was still raining heavily.
So we booked an hour in one of the indoor ones.  The place was okay, but there was mold along the top of the room.  The water was warm enough.  However, the experience paled compared to the ryokan onsen experience we had the day before in Yifuin.
Also, your hour starts immediately after you hand your payment over, including the time you need to take to walk to the next building in the pouring rain.
They need to streamline the process. When you enter the reception area, you need to take off your shoes to walk a few metres to the desk.  After collecting your key, you then have to put your footwear back on to go to the room.  The same process is repeated when you return the key.
Perhaps they should have a rubber pad for customers to walk to the desk and back to the entrance without taking off shoes.