Tepoztlán is only about a 40 minute drive from Cuernavaca either on a Cuota or a Libre thru a few small towns. The most interesting part of Tepoztlán is it's location in a valley surrounded with striking rock formations. There is also a cool church, an ex-convento with a museo and a large market. Other than that, it's a small town worth a few hours.
One of the most interesting side-trips from Cuernavaca is to TEPOZTLÁN , just 20km to the northeast, and dramatically sited in a narrow valley spectacularly ringed by volcanic mountains. Until recently this was an entirely different world, an isolated agrarian community inhabited by Nahuatl-speaking people whose life can have changed little between the time of the Conquest and the beginning of the twentieth century. It was on Tepoztlán that Oscar Lewis based his classic study of Life in a Mexican Village and traced the effects of the Revolution on it: the village was an important stronghold of the original Zapatista movement.
It's also the village where Quetzalcóatl, the Plumed Serpent god of the Aztecs, was born.