Netsu-no-yu Bath
This is the often unbearably hot public bath next door to the yu-batake (hot springs field) that is popularly known as a "fever bath." You can't actually bathe here, but you can watch one of six daily yumomi shows in which locals in colorful traditional garb churn the waters with long wooden planks until they reach a comfortable temperature. You can also sign up for a Yumomi Experience and try churning the waters yourself. It's about 20 minutes of churning and fairly tiring, but you'll be enthusiastically encouraged by local yumomi pros.