Yukai Resort Unzen Toyokan

Yukai Resort Unzen Toyokan, Unzen (Pt.2 - upper baths) From there you can transfer to another elevator on a different floor and get to 5F. There are two baths: one indoor behind glass and a second outdoor one on a balcony (accessed through the indoor one). The view of the buildings is a bit worn (but for me that actually adds to the atmosphere of this place) and there's a clear view of water and mountains. The water feels similar to the lower bath. Likewise had it all to myself. Also highly recommended.

Yukai Resort Unzen Toyokan, Unzen (Pt.1 - entrance and lower bath) A relatively modern ryokan with lots of rooms. Went in the morning - they said day-use starts from 14:00, and both baths are available. 1,030 yen for entry and large towel rental. The elevator system is a bit confusing, but they give you a printed map. Went to the lower one on B1F - a big area with about 20 shower stations and a great view, with a wooden platform in the middle of the bath. The water is milky blue (but not super saturated in color), not much smell, standard water temperature. Had the whole place to myself the entire time. Highly recommend.