Netherlands has about 350 km of coastline (500km if you add the islands) , stretching from Belgium in the south to North Germany in the north. They are all very safe, clean and generally easily accesible. Netherlands has a Nordic climate with few hot days where you can sunbathe. Once temperature hits 25 degrees (Celsius) it seems that half of the country rushes to the beach. Luckily if you are not a big fan of crowds there are enough peaceful gems available. Also, the Dutch have learned to appreciate their beaches whole year long and I would invite you to follow their example. Remember the Netherlands is a small country so you can always combine a healthy beach walk in the morning with a city tour in Haarlem, Amsterdam or Den Haag.