This supersento has been reopened under new ownership. The only big difference is the hot spring well has been shut off. Below is my review while it was under the previous ownership.
Yamato no Yu is a chain of supersentos throughout Japan. They have two near my house in Nishinomiya, and this is the better of the two. The design is typical of supersentos and offers all the amenities such as massage, a restaurant, rest areas, and so on.
The indoor bathing area has a large normal bath and a good maze of jet baths. The two saunas are complemented by a charcoal filtered cold water bath. I really like the way the tile used on the inside floor feels on the feet.
Outside there is a small, but cozy rotenburo area with a small selection of baths. The rock lined tub has many good places to sit. I enjoy cooling down in the 38 degree warm bath the best.
Many of the baths are filled with natural mineral water from a 1004 meter deep well. I was told that there is some fear of pollution by arsenic and other heavy metals in the groundwater here from the factory that was previously built on this location. This must be the reason behind the large poster in the changing room documenting the testing and cleanliness of the water and the boasting of how deep the well is.
This Yamato no Yu is not one of my favorite springs, but it is still good. It does get you hot through and through. Although rather busy, I can earnestly recommend this supersento for a basic, yet relaxing, bathing experience. The location is hard to get to by car, thanks to some one-way roads and hard to make turns.

Update 2019: I have not been since they renamed to Wakara no Yu after the Yamato no Yu chain closed down. The natural hot spring has been converted to a carbonated bath.