Tepoztlan is a very nice and peaceful place to visit. It's famous for its spas, meditation, alternative medicine clinics and a very traditional city center. It is a small town so you don't need a car to travel within the city.
There is an archeological site at the top of an easy-hikeable mountain that is also famous for its "good vibrations".
Temazcal is an ancient mexican therapy that consists on a little igloo-shape room in which a group of people enter and medicinal plants are burned inside it and the place gets really warm. A guide asks people to sing ancient songs to make the experience more complete. Many hotels have this option either in groups or individual.
There are two camping places nearby: Camhomila and Meztitla, both nice and safe.