The energy of Union Square reaches its peak during greenmarket days (Monday, Wednesday, Friday, and Saturday), when more than 140 regional farmers and food purveyors set up shop on the square's north and west sides to peddle everything from produce to meat and fresh fish to baked goods. The market is a great place to rub elbows with—and get elbowed by—local shoppers and chefs and a great source for tasty souvenirs (locally produced honeys, jams, pickles, and cheeses) as well as lunch. Find a bench in the park to savor your goodies and take in the scene. Political rallies sometimes happen here, too.

Even on a nonmarket day, Union Square regularly has vendors of all kinds, selling everything from art to jewelry to T-shirts. New York University students, nannies with their charges, visitors, and other localsgather in this open space that can at times feel more like an outdoor version of Grand Central Terminal than a park. Just south of Union Square, on Broadway at 12th Street, is the Strand, a giant bookstore that attracts booklovers like a magnet.

On September 5, 1882, Labor Day was born when more than 10,000 New York City unionized workers took an unpaid day off to march from City Hall to Union Square.