Tsuru no Yu Onsen

The retro exterior looks like something straight out of the Showa era, but the Tsuru no Yu onsen has clearly been renovated more recently than that, and its interior has the bland functionality of a regular sento public bathhouse. There's nothing to look at but sky from the outdoor rotenburo bath, and be advised that the murky brown kuroyu tub in the indoor bathing area is also electrified (which works as a kind of deep-muscle massage, would you believe). There's an additional tub that lets you try the onsen waters at their original unheated temperature, around 18C.