This complex on the hills overlooking Hakone offers more than the average onsen. In addition to all the water-based attractions, there is a shopping mall modeled on a European outdoor market, a swimsuit rental shop, a massage salon, and game center. The park is divided into two main zones, called Yunessun and Mori no Yu ("Forest Bath"). In the Yunessun side, you need to wear a swimsuit, and can visit somewhat tacky re-creations of Turkish and ancient Roman baths.
You can also take a dip in coffee, green tea, sake, or red wine. It is all a bit corny, but fun. Younger visitors will enjoy the waterslides on "Rodeo Mountain." In the more secluded Mori no Yu side, you can go au naturel in a variety of indoor and outdoor, single-sex baths. When signing in at reception, get a waterproof digital wristband that allows you to pay for lockers and drink machines within the complex.
1297 Ninotaira Hakone-machi, Hakone, Kanagawa-ken, 250–0407, Japan