best way to travel from San Sebastian to Santander to Madrid? Is driving safe? Train service? Thanks!
Without checks schedules I cannot answer your question. But in general the train system in Spain is not as extensive as other parts of Europe. However, Spain has an excellent bus that is cheap, easy, and sometimes faster than the train. So check the bus schedules. Driving is safe but can be inconvenient when it comes to parking.
To get a good answer you need to provide more information. Where are you (if you are) renting the car? How are you getting to San Sabastian in the first place? How much time do you plan on spending in each of the 3 cities? Do you have a desire to stop on the way to each city? You can take the train from San Sabastian to Santander but it is pretty much an all day trip because you have to transfer in Valladolid. The train from Santander to Madrid takes about 4 and a half hours. Personally I prefer trains over buses, you are confined to the seat for the entire trip. Here is a link to the Renfe english website for more train info, http://www.renfe.com/EN/viajeros/index.html