Sunayu

Sunayu locates right by Lake Kussharo in eastern Hokkaido. It is a sandy area with a hot spring underneath. You can dig up the sand in the designated area and create your very own hot spring bath.
There is a also a footbath area for those who want a quick moment of relaxation rather than a long bath.
Between the warmer months (June to September), you can rent out a space on the camping grounds for a few hundred yen a day. You can swim in the lake, bathe in the Sunayu and head back to the campsite for a campfire.