Ixtapan de la Sal is a small spa town in the State of Mexico, south of Toluca on the old road toward Taxco. Its name points to salt and water, and that is still the reason to come: mineral springs, public baths, family water parks, and a slow colonial centre around the parish church.
The town is not a grand colonial showpiece, but it has enough texture for a spare day if you are already in Toluca, Taxco, or the southern edge of central Mexico. Start in the plaza and Parroquia de la Asunción de María, then choose your water: the big Parque Acuático Ixtapan for families, or the cheaper Balneario Municipal for a more local soak.
The best nearby sight is Grutas de la Estrella, a limestone cave system south of town near Tonatico. Combine the caves with lunch back in Ixtapan and an hour around the market and plaza, and the town makes a compact, unpretentious day trip.