The natural landscape of Owakudani is really cool and other-worldly; something akin to Mordor from Lord of the Rings. As you take the cable car up the mountain you get a good view of the smoking sulphuric valley. Once you arrive at the top, you can then continue by foot to take an up-close look at the bubbling pools and steam vents that dot the mountainside. But be warned - the whole area has a very strong sulphur smell!
Owakudani is the perfect activity for an afternoon - after which you can return to Hakone and soak in one of its many incredible onsen!
Note: You should check before planning your trip here, as sometimes Owakudani is closed due to volcanic activity.