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.
The Frank Stella's are the best. They are all over the city and they always look amazing. Two of my favorites are the Saatchi and Saatchi lobby (pictured) and the Citi Corp building in Midtown.
An awesome, and sometimes free, ferry that links Manhattan at the Financial District to Ikea in Brooklyn via Red Hook. Very great views of the city and if you end up having to pay it's redeemable for a monetary discount towards an Ikea purchase. I think of it as a treat and an investment.
The permanent piece called "Meeting" at MoMA PS1 is an etherial experience of light and color and quiet. Sit and look through the cutout in the ceiling and watch the light change both outside and in. You can't tell what you're looking at until maybe a bird flies by.