Best described as an onsen amusement park with a whole variety of outdoor water slides and baths, including wine, coffee, green-tea and sake baths…yes, for putting your body in, not the other way round. Yunessun is mixed bathing so you'll need to bring a swimsuit. The connected Mori-no-Yu complex (11am to 8pm) is traditional single-sex bathing.
Take a bus from Hakone-machi, Gōra or Hakone-Yumoto to the Kowakien bus stop. There's also a variety of accommodation here.