 But the most relevant part for tourists is the carbonated water of "La Laguna Verde", a spring which filters from the subsoil sprouting naturally in form of water eruptions.On January 22, 1981, Ixtapan de la Sal officially became a city.In 1996, it was integrated to the program of the "100 Colonial Cities", which is a touristic program that gathers the oldest as well as the most important Mexican cities.