Near the village Mateiros is so called Fervedouro, is a small well of warm, crystal clear blue water. White sand lines the bottom, forming a natural pool 8m in diameter. The water comes up from the bottom of a pond, filtered through the sand, forming air bubbles in the sand that prevent the swimmer from sinking. The pressure pushes you out of the water. In fact there is no bottom, only a soft mix of sand and water.