Bloemendaal is essentially three things in one: a chain of leafy commuter villages along the railway line west of Haarlem, the open dunes of Zuid-Kennemerland National Park behind, and a long broad beach at the other end of the dunes where the famous beach clubs run their parties through the summer. The wealthy bit (Aerdenhout, Bloemendaal village) is quiet and residential; the wild bit (the dunes) is open and beautiful; the loud bit (Bloemendaal aan Zee) is loud.
For a day trip from Amsterdam or Haarlem, the standard sequence is: walk or cycle through the dunes from Overveen station to the coast (about an hour), spend the afternoon on the beach, and either party at the beach clubs or take the bus back. The 19th-century country estates of Elswout and Caprera, and the village of Aerdenhout with its Art Deco curiosities, are worth a detour if you have more time.