Thermal bath = Japanese call "Onsen"
Onsen list
1,Nyuto Onsen (Akita)
Spa and Snow resort. One of a good onsen
2,Kusatsu Onsen (Gunma)
Spa and Snow resort.
3,Manza Onsen (Gunma)
Spa and Snow resort. you can take a free bus to this onsen from Tokyo.