While open, accessible, and beautiful year-round, a summer visit to Copenhagen isn't complete without a trip to Amager Beach Park with its large white-sand beach. This park/beach is hugely popular with locals and visitors who enjoy BBQing, drinking, sunbathing, and relaxing along the beach's shores. Despite its proximity to the city, the water is extremely clean and safe.
A favorite tradition among locals is to head down to the beach and then pause for a double scoop of delicious ice cream. Despite their location and the high demand, most of the vendors keep their prices reasonable.
The park is easily accessed via either the Øresund or Amager Strand St. stops.
Copenhagen (and Denmark) are famous for being incredibly environmentally friendly. Windmills play a huge role in making that possible.
One of the best places to see the large windmills installed just off Copenhagen's coast is from the beach at Amager Beach Park. I find that the fact that they are marine windmills makes them even cooler and more fascinating than those installed on land.