The Yubatake in Kusatsu is like the hot water heart of the town. It's where all that natural, bubbling hot spring goodness comes from, and it's pretty darn productive, pumping out 5000 liters of hot water per minute! The wooden conduits cool down the water a bit before it gets sent off to the ryokan and public baths. Plus, you can soak your feet for free in the foot bath and stroll around in your yukata and geta sandals at night.
This is an awesome place for Christmas time as they have a good festive vibe with the place illuminated during the winter.