Tepoztlán is famous for being in a lovely location, being the birthplace of the god Quetzalcoatl, and having a temple/pyramid to the god of pulque (some sort of fermented drink). The New Agers have set up shop here, and you can additionally enjoy a lovely spa experience, buy incense, and have your aura photographed.
Saturday is Market Day, so in addition to crystals and the such, on the other side of the square you could do your everyday shopping. The butcher shops were the best. Zorra pointed out a strange blemish on one of the pieces of meat hanging there -- yep, Bessie's eye.