From San Sebastián to Vitoria is a bit tricky since it is all hills, i will print a map my sugestion. From Vitoria to Marugan a straight línea is perfect, thought altitude is increasing above sea level ( Burgos altitude is 3000 ft) there are no hills nor montains except to the east, so you can fly 1000 AGL in flat to Marugan.
Marugan is close to Segovia City, north of Madrid, there are some montains between Madrid and Marugan, but only you have to cross them if you are coming from the south, it is not your case.
I will try to print the flight from san Sebastián to Vitoria. I worldwide soy tris is the tricky zone from France to Marugan.
Best regards,
Miguel