sauna mounted on a small truck
A portable sauna built into the bed of a kei-truck (軽トラック). Often used at outdoor events or rented for private use.
A truck-mounted sauna had come to the event venue.
Recently, more people are renting kei-truck saunas.
Compound of 軽トラ (kei-tora, abbreviation of 軽トラック 'light truck') and サウナ (sauna).