Warm-water pool with a bench where users could rest their backs. The water was heated with a furnace or praefurnium attached to the pool which was always left on. The warm air from the furnace was conducted to a deposit or hipocaustum located under the alveus, so the water was heated by steam. Next to the pool, visitors can see a mosaic with dolphins that framed a cool-water fountain or labrum, which allowed users to cool off while they were in the caldarium.