Arcos del Sitio is a long 18th-century aqueduct in the countryside northwest of Tepotzotlán. The stone arches were built to carry water, but today they work as a scenic day-out spot with picnic areas, walking, riding, and zip lines.
It is not in the town centre, so plan transport rather than assuming you can casually walk there. The aqueduct is worth the effort if you want Tepotzotlán to be more than a museum-and-lunch trip.