This modern, family-oriented complex is more like an onsen amusement park, with outdoor water slides and a variety of baths (including some filled with coffee, green tea and even sake!) as well as indoor swimming pools with a retro leisure centre vibe. Mixed bathing so you'll need 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.