As already mentioned, the drive is mostly highway and will take closer to 4.5 hours. Once you leave Portugal there are no tolls to get to León.
The shortest route has one entering Spain by Puebla de Sanabria. It is a small town with a nicely restored small castle and plaza mayor. There’s also the Iglesia de Santa María del Azogue. Continuing towards León in Astorga is Palacio de Gaudí if you’re a Gaudí fan. There’s also a cathedral that is a museum beside the palace. There’s little else to the town. A large free parking lot is at the bottom of the town. From Astorga to León there is a toll road, but it can be avoided by taking the local, 2-lane, N-120 road that parallels the highway.
If you take a different route to León you’ll pass by Valencia de Don Juan. About 5 miles off the highway is Castillo de Coyanza Valencia de Don Juan that looks fairly impressive from the exterior. It was closed when we stopped, so never made it inside.
In both Puebla de Sanabria and León we stayed at the Paradors in each location.