Dia:Beacon is a short train ride from the city in a former Nabisco box printing factory. This art foundation has 240,000 square feet of art from the 1960s to the present. Dia features the work of Sol LeWitt, Imi Knoebel, Andy Warhol, Dan Flavin, Agnes Martin, On Kawara, Bruce Nauman, and many others. I love going during the summer to enjoy the gardens surronding the building.
Nothing is more quintessentially New York than a diner. This eatery not only serves excellent, traditional diner fare, but does so in an eclectic environment that mixes Baroque decadence with Midtown grit.
Part of the Marlow restaurant group, Diner is one of the more casual / rustic options. The menu changes daily and is written out (most likely upside down by the wait staff) on your table or the back of a receipt. The only constant item is the burger, which to be honest, is one of the best in the neighborhood. If they have a breakfast sandwich for brunch, get that. The fried chicken sandwich (with dark meat) is also a favorite. They make scrambled egg dishes better than most. Dinner is solid all around (they crush a steak for two). Homemade ketchup and dijon mustard are on every table, so regardless of what you get, these two condiments are worth the visit.
Erie Basin is a really wonderful little shop full of old, creepy and beautiful things, such as Victorian mourning jewelry (some with hair in it), Freemason masks from the 1900's, tiny children's rings from the 1700's, and all kinds of other treasures. It is really as much a museum as it is a store, and all of the items have a haunting and unique aura.