As it turns out this is a hotel motorhome taking some German visitors around the US.
Each little window is a bed compartment like you would have on a train.
The front part is a bus with seats for the passengers to ride in during the day. Underneath they had a full kitchen, with a stove, refrigerator and all the equipment they would need.
the one side slide out for additional room. They set up tables and prepared their evening meal.
Nothing like taking your hotel with while you are touring another country.