Like the other day use hot spring next door, Yakushi-yu is absolutely outstanding. Starting from the Taisho era architecture to the amazing bath coated in years of sediment from the spring here. Oh and the spring here is extra hot so take breaks. One of the most real and unfiltered true hot spring experiences you can have in Japan. There is a fountain with drinkable spring water in the parking lot next to the building. Remember that this is a very rural city so be careful about the train time table and that there are not many shops in the town. Also, it's a good walk from the train station so time your bathing appropriately.