I’ll assume you will have a vehicle. If coming from the Madrid’s airport, La Granja is an hour’s drive if coming over the mountain via Tres Cantos and Colmenar el Viejo. There are no tolls along that route.
The main attraction in La Granja is the Royal Palace of La Granja of San Ildefonso. For me it wasn’t one of the better palaces I’ve visited and I could easily have skipped it. The gardens, especially in the spring should be beautiful if plants are in bloom. The gardens were free to enter while there was a charge for the palace. There’s little else to the town and one night was sufficient for us. With two nights you could easily visit nearby Segovia.
If looking at Google maps it looks like there is dedicated Parador de Granja parking across the street. As an FYI, it’s a free public lot and not just for Parador guests. Depending on when you arrive in town, you may need to wait for someone to pull out. We parked in a non-spot for a few minutes until a real spot opened up.
The Parador de León is a beautiful building. Set your navigation system to Plaza de San Marcos and it should take you right to it. Parking was free when we were there and on the backside of the Parador. While there, visit the Convento de San Marcos beside it. The Camino de Santiago passes directly in front of the Parador. From it we walked all around town.
Since you’d like to try Paradors, a Parador just south of Burgos (no Parador in Burgos) is in Lerma. It is a small town that is conveniently located if you wanted to visit Burgos, Aranda de Duero, or Covarrubias (on Span’s prettiest village list). If the teens have seen The Good, The Bad, and The Ugly movie, the site used as Sad Hill Cemetery is nearby, as is Monasterio de San Pedro de Arlanza whose interior was used in the movie and Campamento Betterville that was the civil war camp in the movie. If you enjoy nature walks, Desfiladero de La Yecla is a 30 minutes drive from Parador de Lerma and very near the movie filming sites.
