Very unique wooden and old-style onsen experience. I was told there are few onsens of this kind still around. We were there during a heat wave so there were few people around. The male and female baths are separated but there are, if I recall correctly, two ways to be co-ed (which is for families and couples.): One is that the lady goes to the open air part and invites the gentleman over to that part. The other is using a special smaller private onsen area by getting a key to that part. So it is not German style co-ed where naked strangers co-mingle. The place is low-key and no frills so if you need hair dryer, shampoo, etc, etc., this is not for you. If you are like me and walk to 7-eleven at 3am in search of head ache relief (perhaps due to smashing oversized forehead into low doorways), then if you find yourself out at that time, look up! You are far enough away from Tokyo to have the heavens above stuffed with stars (which might explain why there is an observatory-looking thing on the grounds of the onsen)

Kanaya Onsen Ryokan, in Rendaiji, Shizuoka, has both segregated and mixed baths. Founded in 1866, it is famed for its indoor baths, particularly its mixed bath. The mixed baths are inclusive, yet access to the baths, for ladies, is through  a rustic wooden door that is lockable, and one-way.  Ladies have exclusive access to three keys to open this door. If the key is misplaced during the bath, there is no way for the female bather to get back to the ladies changing area. Lol! The large indoor mixed bath, built in 1915 and renovated in 2002, is 15-metre long and 5-metre wide, with two depths of about 600-millimetre, and 1-metre. The windows are water-to-ceiling height, and the waters  are clear and hot! The female indoor bath, built in 1991,  is smaller at about 11 metres in length, with a 5-metre width. The bath, partitioned to offer varying water temperatures, offers  a high ceiling wood structure. Access to a modest size outdoor mixed bath of about 4 by 5 metres, is through another quaint wooden door. At first glance, one would assume that the only way to get to the other side is to stoop very, very low and squeeze through a narrow gap below the door. :p Thank goodness this was not to be. The door actually hangs about 1-foot above the water, and with a slight push, up a flight of steps, we embraced the sun and soaked in the not-so-hot waters. Amenities-wise there are coin-operated lockers and hair dryers. In the bathing area, shampoo and body wash are available. We brought our own onsen towel, a bottle of spring water, and it was fun! Psst! Whilst there, we saw a beautiful full-body tattoo on a guy. He and other guys were being entertained by a lady in the bath. It is refreshing to know that this bath is tolerant of body tattoos or did they sneak in surreptitiously? :p

A real gem of a Ryokan & Onsen. For all of you who are into old style, tradition and japanese beauty - this is the place to go! You can visit the Onsen without staying at the hotel.

Great Onsen with a huge and nice old fashion Japanese style bath. Women are allowed to enter into the men's bath, not the opposite. Has an indoor and an outdoor part and you could even swim! People with tattoo weren't tell off which is a good thing. When I went everyone was Japanese apart of me. Recommended.

Sen-Ninburo (A thousand men bath) is an old hot spring that offers a gender-mixed indoor bath and also a ladies-only bath. The main bath really resembles a swimming pool and, because it was built many decades ago, it's deeper than any other hot spring that follows the current standards. Definitely it's a rare place.

There are no shampoo and conditioner, only soap bar for body. Hair dryer is not free too. There are only 2 shower stations with shower hose, the rest are just taps only. This cost 1500, too over price. If you want to clean yourself thoroughly, this is not the place to go. Only good for soaking. Tattoos are allowed which is awesome.

Atmospheric large wooden bath with option for mixed bathing (ladies need to come to men's side)

Very good onsen to go to. You can feel the Japanese culture there. The while bath is made of wood, this is very spacious and deep for a Japanese bath. There is even a connexion to an outdoor bath. I really loved it. I highly recommend.

Went for higairi-onsen, 1500yen, was quite small but overall great place

The onsen was one of he top five I have been to in all of Japan. They have two sources of onsen water that are different temperatures, and the bath itself is absolutely beautiful! Wooden and glass interior with beautiful patina. I would recommend this place to anyone who wants a refined and classic Japanese onsen experience it's 800¥ for he bath and they sell towels for 200¥. There are only bars of soap inside, though- that's why the four stars instead of five. No shampoo or conditioner. Women can also go into the men's bath if you're brave!

The public bath is ¥1500 in the summer. I totally enjoyed using the bath.