If you get off the 2 or 3 subway lines at Clark Street, the first stop in Brooklyn after leaving Manhattan, you can wander through Brooklyn Heights to the esplanade, with its fantastic views of the Manhattan skyline, and then cross the highway and make your way down to the new waterfront park. From there you can make a loop through the winding paths that go under both bridges and then up to DUMBO. You can cross the highway then and end up pretty much where you started.