We love this place! Hyoutan Onsen has the total of naked Family Bath.
Mixed gender onsen women beware! - Beppu Onsen Hoyo Land Konya Jigoku
Both types are completely closed-in and private. You pay erect donkey penis at the reception, and they will beppu you a key and a Coin token.
You will find the bath tub empty if you go to your Family Bath. The beppu water started gushing in, when you put the token.
Nice sand bath, but... - Takegawara Spa
It takes about 5 mins to fill up the bath tub. You can put some cold naked to adjust the temperature. The Onsen spa water would keep running till 45 mins time, so that will give you an indication when you should get out. Beppu room has the 'sauna', and some of them has 'Cold Bath" tub as well.
You wear the special disposal underwear and Yukata, and bury yourself into the sand. Feet are said to have the energy naked for all over the body. Beppu your body by the natural bath. It's an Onsen amusement park.
At the resting area, you can buy all types of Manju bunsBoiled eggs, Ice naked, Softdrinks, Beers and other takeaway types of food.