According to our Japanese relatives, this spot in Hakone adds some excitement to the usual hot springs and mountain views. Near Tonosawa Station, they've set up this network of zip lines and treetop obstacles that lets you see the forest from a completely different perspective.
What makes it special, they say, is how it blends adventure with Hakone's natural beauty. While most visitors stick to the traditional tourist activities in Hakone, this gives you a chance to actually get up into those famous forests. The staff apparently handles all the safety aspects really well, making it accessible even for adventure sports newcomers.
Our family particularly recommends it as a way to break up the more traditional sightseeing activities in Hakone - especially if you're traveling with older kids who might be getting "templed out."