If you have your own wheels, head up through town past Jigoku-dani and keep going on Route 350 as it becomes a narrow mountain road. Eventually, after about 8km, you'll reach Kuttara-ko, a circular volcanic caldera lake which is remarkable for two things – there's not a single river flowing into or out of it, and it has been left almost completely untouched by human hand. Lap up the natural environment before carrying on back down to the real world.
