Many subway lines connect to the Financial District. The Fulton Street station is serviced by eight different subway lines (A, C, J, Z, 2, 3, 4, 5) and puts you within walking distance of City Hall, South Street Seaport, and the World Trade Center site. To get to the Brooklyn Bridge, take the 4, 5, or 6 to Brooklyn Bridge City Hall.
For sights around the New York Harbor, take the 1 to South Ferry, the R to Whitehall, or the 4 or 5 to Bowling Green. The 1 subway line stops in the heart of TriBeCa (Franklin Street).