Clean water and white sand
The Iberian Peninsula is full of great beaches. Endless, really. I was in Santander in March, so you can understand if I wasn't too eager to go for a swim. However, sitting on the sand enjoying the sea air and some heat from the midday sun is a pleasure you can't get enough of.
Noja Beach is a beautiful stretch of coast with desert-like white sand. I recommend visiting if you're in Cantabria.