The building was built in 1938 and has become a hot spring with a luxurious roof with a “Karahafudukuri” (you can see the image on Google, just copy “唐破風造” and search) and its appearance is a symbol of Beppu Onsen.
The hall reminds you of early Showa era(1926–1989) and has become a space that you can relax after bathing.
Also you can enjoy a sand bath there.
The 3rd Wednesday of December
The 3rd Wednesday of each month