Though not blessed with the sheer number of sights that Manhattan has, Brooklyn does have more than a few interesting museums, parks and gardens that make for excellent visits. But some of the best sights in Brooklyn are the neighborhoods themselves, many of which are perfect for casual strolling – you can get a feel for local life, admire 19th-century brownstones, pop into eclectic shops for a browse, and indulge in food and drink at Brooklyn's wealth of great restaurants and bars. Also unbeatable are the views of Manhattan from numerous vantage points along Brooklyn's shores.
If Brooklyn were its own city, it’d be the fourth largest in the US by population – with more than 2.6 million residents, it's bigger than Houston, Philadelphia and Phoenix. Sprawling over an area of 71 sq miles, Brooklyn is essentially split in two transport-wise, with one set of subway lines servicing the northern half of the borough, and another set traveling to points south. So if you think you can see all of Brooklyn in a day, think again.
If you're just going for a day trip, it's best to pick one neighborhood or section and stick to that. The waterfront area of brownstone-studded Brooklyn Heights offers lots of history and great Manhattan views (and an easy ride from Manhattan). Fans of vintage amusement parks and beachside strolls should head to Coney Island. For the night owls, the trendy enclave of Williamsburg lies just a single subway stop from Manhattan and is loaded with bars, restaurants and live-music venues. Prospect Park is just as magnificent a green space as Central Park (and only slightly smaller), and many of the residential neighborhoods surrounding it are great for architectural walks and cafe-hopping.
There are some areas of the borough that can get a bit sketchy, though, so if you're planning to explore off the beaten path on your own, ask around first.