I fully recommend everyone who visits Oaxaca to also visit Hierve el Agua. With its natural beauty there are two impressive petrified waterfalls here (calcium carbonate), that were formed thousands of years ago, as the result of dripping carbonated water. The water descends 160 feet (50 metres) over two rugged rock cliffs. Water temperature is slightly above air temperature, fluctuating between 71 and 77ºF (22 and 25ºC), and therefore much below the boiling point mentioned in its name.