Tlayacapan is a small town in the state of Morelos close to the waterpark city of Oaxtepec (a combi away - MXN$9.5). It is one of the many cities with a former convent that is a part of the UNESCO heritage site for the former missions on the slope of Popocatepetl. I couldn't see the volcano, however. The main church wasn't that special to me, as I find the many little chapels scattered around the city to be its gems. There's a municipal palace in the centre, but it seemed to be severely damaged by the earthquakes in 2017 and never rebuilt.
Very walkable city. Would recommend as a day trip.