Lake in Noboribetsu Onsen

If you have your own wheels, head up through town past Jigoku-dani on Rte 350 as it becomes a narrow mountain road. After about 4km you'll reach a lookout point for Kuttara-ko. This circular volcanic caldera lake 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 hands. You can't drive any further, as traffic has been cut off to protect the lake.