The mythology says that a monk recovered using the hot spring here.
The mythology says that the water changes color 7 times in a day.
The mythology says if you bathe here when you're pregnant you will have a healthy baby.
All you really need to know is that this is one of the most amazing places in Japan. There is something very special about this place, especially if you can share it with someone you love like I did. The water leaves you skin feeling as if it was coated in soap. Afterwards, this bath will leave you feeling better than you could imagine. I can't wait to go back.
Because only two people can use the bath at the same time, you have to make a reservation and wait your turn. Men and women can enter together and children are also allowed. What you do is go up to the ticket counter. The person will give you a general idea about how many people are waiting in front of you, but they won't tell you how long the wait is because they don't really know how long everyone will take. Coming earlier in the morning increases your chances of getting in sooner. We got there around 9 AM and were able to go straight into the bath. Great luck.
After you buy your tickets from the vending machine, the front desk person will give you a plastic card with a number on it. They will call your number when your time comes up. If you're not there then they call your number you will loose your turn, so make sure to stay in the area. After your number is called walk along the river to the shack that surrounds the bath. In front of the door place your number on the hook in view of the CCTV camera, take off your shoes, and enter.
Inside there are some plastic baskets for your clothing. Of course you go in naked like any other bath in Japan. Since there is no place to wash with soap a simple splash off is fine. That's what I did. I think that using soap isn't allowed in Tsuboyu, but I might be wrong. The natural well water is a boiling 92 degrees C so you'll have to add river water from the large gray pipe to cool the bath before you can enter it. There is also a large stick there for you to use to stir the bath. The hottest part of the bath, where the hot water bubbles up to the river bottom is in the upriver corner. The tub is mostly made up of a worn smooth doughnut shaped stone that makes a dam like wall keeping the hot water in. The upriver side is made of a natural and man made rock wall. The bottom of the tub is filled with smooth river rock. You can't see the bottom, so make sure not to drop anything into the tub as you most likely won't be able to find it.
After you leave the main Tsuboyu, you can use the medicated baths behind the ticket booth. We didn't try them.
While your waiting, or after you get out I also recommend getting eggs from the nearby stores and boiling them in the onsen water. They come in a net to boil them in. It takes about 15 minutes for the eggs to boil. The adjacent ryokan cook bamboo shoots and other vegetables in the water here for their guests.
There is also a simple public bath, men and women separate, that you can use with out waiting. The water is not the same as that in Tsuboyu, but it’s very nice.