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.
The Future Perfect is my favorite place to shop for furniture / interiors, or pick up a small gift for a friend. They have a perfect mix of beautiful and strange objects, some of my favorites include the Animal Butt Magnets, Shrigley Salt & Petter Shakers, and the Bank in the form of a Pig.
For brunch, the classic dish to get is the Feijoada, but the benny is also solid (and i don't recommend a benny lightly)—you can also ask for ham and spinach together (my favorite). For dinner you can also get the same thing, or the Moqueca (shrimp stew) is incredible. Pro-tip: if you're there for breakfast on a weekday, ask for a egg and cheese (add bacon or ham or avocado) on a croissant. Not on the menu—sounds basic, tastes amazing.