Calpan is a small town in the state of Puebla in México, accessible by a combi from Reforma, Puebla City via Cholula and Huejotzingo (one bus every hour - this means the fastest way to get there from Mexico City is via a coach to Huejotzingo then take the combi). It's one of the many towns in Puebla and Morelos with a former convent that's a part of the UNESCO heritage site of former missions on the slopes of the volcanos.
Beyond its small historic centre, with the convent, the main church, the volcano (which was actively erupting), the main square, and the cemetery, there's not much to see there. It was however nice that the former convent was one of the very few that's not under maintenance.