In Yamanashi, possibly we have about 500 or more onsen (hot spring) facilities. When you go into any public onsen facility, you are supposed to follow some Japanese ways of manners.
I suggest you to take both long towel and short one as well. If you have a short towel with about 10 by 30 centimeters, it is perfect. Usually, at each onsen facility, you can buy the towel in case you forget to bring for just 100 to 200 yen for each.
After you enter the onsen facility, you pay the fare and go into the dressing area where you take off all your clothing. Usually, they have a certain number of lockers where you can keep your important personal belongings as well as your clothing. Sometimes you might need to insert 100 yen coin to use the locker. Yet, this 100 yen coin will return to you when you use a key to open it later.
Usually, at the dressing area and also at the lobby or in either spot, there are toilets that you can use.
After taking your clothing off, you can open the door and go into the "bathroom" but you had better take only a small towel with you. For a long one, you just leave it with your clothing.
(1) Whenever you open the door between dressing area and bathroom, you should quickly close the door.
(2) First, you have to rinse all your body at a washing spot before you enter the bathtub.
(3) You should NOT take your towel inside the bathtub. You can keep it on the shelf, the corner of the tub in the bathroom, though, or place it on your head.
(4) Usually, for the use of shampoo and body soap, they are set up in the bathrooms and you are allowed to use them. Sometimes, people take their own toiletries so you have to be careful not to use them, though.
(5) When you wash your body and hair, you should NOT do it while standing. That’s because the water that you use for taking shower might go to people behind you.
(6) Before you come out of bathroom back to dressing area, make sure you dry your body with the small towel that you have. Otherwise, the water drops from your body on the floor and the floor gets wet. It is NOT good for others. After you come out of the bathroom, now you can use a long sized towel to dry your body and hair completely. In case there is a hair dryer provided by the onsen facility at the dressing area, you may use it.
(7) While you are at the facility, you should NOT talk aloud. That might cause a trouble.
(8) For those who have long hair, you should tie up your hair or wear a swim cap to keep your hair away from the bath water.
(9) Do not wash your personal items in the sink in the area of your clothes.