The Miami Beach boardwalk begins at Indian Beach Park at 46th Street and Collins Ave. It continues south to 23rd Street where it becomes a paved surface. The paved portion of the boardwalk continues through the Ocean Drive Promenade to 5th Street. South of 5th street there is also South Pointe Park which provides nice views of the port of Miami (Government Cut).
Walking your dog on the boardwalk
Technically, pets are prohibited in public parks and beaches. See Miami Beach City Ordinance Section 10-10. However, at any given time you can find people willing to risk the small fine by walking their dogs on the boardwalk (south of 21st street) with leashes.