Lower Manhattan is the southernmost part of the island of Manhattan (downtown Manhattan) - the main island and center of business and government of the City of New York. The lower Manhattan business district includes Wall Street, City Hall, the Municipal Building, the Financial District, and the site of the World Trade Center. Before the terrorist attacks on September 11, 2001, the Twin Towers were major New York icons. The area also contains many old and historic building and sites.

Sources, related links:
Lower Manhatten Information
A neighborhood map of Lower Manhattan