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!
Apart from Dia Beacon, in Beacon (upstate New York about an hour away from Grand Central Station) and also the Judd Foundation in Soho, this institution is absolutely one of my favourite places to visit and it is located in Long Island City, Queens. It showcases sculpture in the broadest sense and has an incredible building that used to be a workshop that refurbished and fixed subway cars. It has been running since 1928 and when you visit you will definitely see why that is.
Little skips is my place when I need to refill my energy with some morning sunlight. The big windows facing the street let all the light in while you can drink some coffee.
My favorite thing to eat is the grilled cheese sandwich with some avocado. Out of rush hours or weekend mornings, it's a pretty good space to take your laptop and get some work done.