The Leguna Cejar is a wonderful experience and a must-do if you are in San Pedro de Atacama!! It is amazing being able to float with no effort at all. Be sure not to put your head under the water as the salt concentration is high and really stings in the throat and nostrils. It's not necessary to take a tour as you can just drive and bathe yourself with your own/a rented car. It is a small fee - around 2,000 Chilean pesos to enter the National Park but well worth it. Be sure to bring lots of sunblock and fresh water to wash the salt off your body after the swim.