As the summer is my favorite time of the year and that the beach is just 15 min bikeride away, I recommend Amager strand. Full of people usually though, but even so it gives a bit of an exotic touch to such a scandinavian city with the sea and the bright sand in the hot summer days.
Between colony gardens in Amager lies one of my favourite local spots: Baghaven. Good food and cosiness is in the forefront. Various events with and without music gather people on the square at Diamantgangen 75. A very local experience. Great for families, children, young and old.
Cinemateket is a really amazing cinema. It doesn’t show any new releases, but always has an interesting program that takes starting point in either a period in the history of film, a director, an actor/actress or another theme.