Alternatively and even better, you could stay in the old town (example) or nearby for a night or two in one of many equally ancient (but renovated) posadas, pensiones or hotels.
Santillana del Mar is well located for exploring the best of central Cantabria including Comillas of course, but also the Picos de Europa and some magnificent Cantabria beaches, though sadly, in spite of its name, Santilla del Mar is not by the sea. Suances is the nearest beach about 15 minutes drive but parking there after 10. 30 am in the summer will be impossible. We tried and failed, but other better beaches are available a short drive away, with parking.
A medieval bar and icecream shop overlooked by an extravagant coat-of-arms, a common feature of Santilla.
We knew that other tourists (mainly Spanish) would infest the streets of Santillana in the summer months so we decided to get a relatively early start from Santander – which in Spain isn’t too difficult as they eat late, sleep late and start late in the morning.
Unfortunately our cunning plan didn’t take into account delivery van overload, so we had the gorgeous old calles and casas to ourselves at about 9 am – apart from a dozen white vans parked here and there doing their delivery thing but not helping to deliver atmospheric photos. By 10 am, however, the vans had gone, to be replaced by not too many sightseers. They would come later. . .