I discovered the Frick my first week in New York, during a heat wave in August. The galleries were surprisingly empty, with only the occasional visitor strolling through the rooms, gently creaking the floorboards. I stood for a while in front of the Bronzino, a portrait of a boy standing against a background of green drapery, and then sat in the courtyard for a long, cool hour.
This place is amazing. It's a short walk from our apartment and has an amazing happy hour including cheap guacamole and $4 margaritas. We can spend an hour or five hours here at a time because the environment is so casual, welcoming, and the food is just damn good. Get the lengua or the camaron al mojo de ajo tacos or hongos and rajas con papas if you are vegan.
Seasonal salads, sweet and savory treats, and great coffee. It's probably my most common lunch spot when I work from home and they also offer catering if I'm too nervous to cook but want it to feel homemade.