It's so cold this winter in Japan. I'll recommend you the experience of "onsen."
The Japanese word "onsen" means "hot springs." Atami-city is famous for its hot springs, and it's not so far from the capital Tokyo. It takes only 32 minutes from Shinagawa, Tokyo by super Express "Hikari."
You could see much about the Japanese 'onsen' from the article of CNN.com. Please see from the link below.
"Healing waters: The Japanese onsen experience" (CNN.com)
21 December, 2012