Day trips
Parras de la Fuente, Coahuila
Be honest about the geography
Parras sits alone in the desert between two cities, so day trips mean real driving. It is better treated as the destination itself rather than a hub for hopping around. That said, a few things are within reach if you have a car.
Saltillo
About two to two and a half hours by car. The Coahuila state capital has a genuine historic center, the Desert Museum, cathedral, and a real city dining scene. It is a worthwhile day if you want a change of pace from the pueblo, though the drive each way eats the day. Better as a stop on your way in or out than a same-day round trip from Parras.
Torreón and the Comarca Lagunera
About two hours by car. Torreón is a larger, workaday city, useful mainly if you are flying in or out or want big-city amenities. Not a scenic day trip in itself. Skip it unless you have a reason.
Around Parras itself
Honestly, the best “day trips” are the short hops within Parras: out to Casa Madero, and to the different balnearios and springs on the town’s edges. These are minutes away, not hours, and they are what you actually came for.
The verdict
Do not build your Parras stay around day trips. Use your two days on the winery, the pools, and the town. If you want a city day, fold Saltillo into your arrival or departure rather than backtracking.