Day onsen near Hakone-Yumoto where the appeal is really the outdoor baths which offer views of the trees below. Tends to get crowded which detracts a little from the natural surroundings, but certainly an onsen to remember when you visit Hakone.
Hakone Yuryo is a traditional day onsen located near the Hakone-Yumoto, the gateway town to the wider Hakone region. It has a variety of outdoor baths offering excellent views out onto the woodland and forest that surrounds the onsen. The onsen also offers private open-air bathtubs for ¥3,900-¥5,900 per 60-minutes (up to 4 people). Bookings can be made up to one month in advance over the telephone.
The other thing for which the onsen is notable is its löyly sauna service. Löyly is the Finnish word for the wave of steam that hits your body after water is thrown on the hot rocks in the sauna. In Japanese this word is roryu, and it is used to refer to a service offered at some onsen whereby (after throwing water on the rocks) a member of staff takes a large fan, stands over each person in turn, and wafts the hot air at the top of the room down onto your body. After having done this for each person, the sauna is then heated up further and the process repeated a total of three times with the heat at around 80°C.
When I was there about 15 people entered the sauna for the service. A couple left after the first round, and everyone of us darted out of the sauna immediately after the second wave of air hit our body. The third wave is not the faint-hearted. This free service is held every hour from 11:30 to 19:30. The scent of the sauna is also changed on a daily basis (e.g. lemon, mint, wine, and peach).