Going for a stroll on Atlantic Beach is a fall Sunday must. I rarely go to the New York beaches in summer because of the crowds, but standing on an empty, windy beach is a total mind soother. Make sure to take a peek at the Miami-colored Catalina Beach Club. Beaches close mid-September.
This is a pro tip, but also a summer tip, take the ferry from Lower Manhattan to Rockaway and spent the day. The beach is great and the area is impossible to gasp that it's 30 min from Manhattan (without traffic) - Eat as many tacos you can, cause it's the best in the state of New York!
This is a great park, from free concerts to summer to the Brooklyn flea markets over the weekend or take the ferry across the river. Rain or shine I never get sick of that view.