Third Avenue is a north-south thoroughfare on the East Side of Manhattan in New York City, running in that borough from East 4th Street north for over 120 blocks. Third Avenue continues into The Bronx over the Harlem River north of East 129th Street. Third Avenue carries only northbound (uptown) traffic north of 24th Street, south of which it is two-way. Manhattan is an island bordering the lower Hudson River. ... Midtown Manhattan, looking north from the Empire State Building, 2005 New York City (officially named the City of New York) is the most populous city in the state of New York and the entire United States. ... The Bronx is one of the five boroughs of New York City in the United States. ... The Harlem River, shown in red, between the Bronx and Manhattan in New York City The Harlem River is a tidal strait in New York City that flows 8 miles between the East River and the Hudson River, separating the borough of Manhattan from the Bronx. ...