白根山 (Mount Shirane) and 草津温泉 (Kusatsu-onsen) are both in 群馬県 (province of Gunma). For my first trip there, the 9 of us we travelled from 東京 (Tokyo) in a mini-van, which took approximately four hours. The memory of the day is the incredibly emerald-green crater lake 湯釜 (Yugama) at 白根山 (Mount Shirane). Following a rest, we hiked around and even saw snow and ice. Later, we drove to 草津温泉 (Kusatsu-onsen), and attended a show featuring a traditional dance called 湯もみと踊り (Yu-momito-odori) created to cool down the water of the local hot springs. Finally, we enjoyed a relaxing time at 草津大滝乃湯 (Otaki-no-yu).
If you want more information about the area, please check the guide page for 群馬 (Gunma).