At an altitude of 1,500 metres, the Vall de Boí has several healing mineral springs with temperatures ranging from 4 to 56 degrees. The Romans already appreciated the therapeutic virtues of these lands in the first and second centuries, as did the lords of Erill, who ruled these lands a thousand years later, but the first Bath House as such was not built until the seventeenth century. Today, the historic Balneari de Caldes de Boí has 37 thermal springs with waters that naturally feature chlorine, sulphates and calcium bicarbonate. It also has two hotels that open from spring to autumn, and a well-known bottling plant for mineral water. It is the spa house with the widest variety of waters, a fact that has earned it a place in the Guinness book of world records.