Summer in Prague isn't long, but it is beautiful, and Czechs like to spend as much time as possible when the good weather finally comes along. Parks fill up in the evenings, and second run movies hit the park in Karlin!
If you missed a movie in the first run at the cinema, or just want the pleasure of a place outside to watch a movie with some tap beer (it's Prague, so obviously there will be beer) then head to Karlin in the evening! There is a movie every day at 9:30. They're usually in English unless noted on the schedule and it's 50 czk to get in.
Gates open at 8:30, for popular movies there will be a line and seating is limited!
Su-Sa: 20:30-00:55