When you leave the dock area you need to turn to the left but the one way system means you turn right and then double back at the first roundabout. The road goes through a built up area for about a mile and then opens out into the motorway. You need to take the A67 and keep with it until you reach junction KM103. From there you need to go across country on N627 following signs for Burgos. As you approach Burgos avoid the city centre so follow signs for Madrid. Eventually you'll join the A1 and you'll find Camping Pico de la Miele at junction 57. You'll have covered around 230 miles and you'll need 4.5 hours or so (without breaks) for the journey. You didn't say what your arrival time was in Santander, but my next one is at 5.30 in the evening, so I plan to stay overnight at Camping Virgen del Mar in Santander, giving me an early start the next day.