This is, of course, in Japan—a nation with a firmly well-developed and established bathing culture. The Sabus (sauna bus) is operated by the Shinki Bus company in Himeji City of Hyogo Prefecture. The bus, sadly, does not offer a sauna while you are travelling on it. This bus is decommissioned and permanently parked in a lot. But you can visit, undress in tents, and enjoy a steam from a wood-fired stove.
Sora News 24 dispatched a reporter to investigate the experience. Sadly, the popular Sabus was already booked, so the reporter was unable to gain access to the interior. But he was able to take photos of the inside and outside of the facility.