Marking dangerous coastlines, shoals, reefs or rocks, these light (or sound) emitting structures hace offered a navigational aid for all mariners for millenniums. There are approximately 1000 lighthouses throughout the United States, with Michigan having past and present over 150 lighthouses, the most in one state. While today's technology has made many of these beacons obsolete, their popularity has helped save many of them from disappearing.
Alphabetical list of U.S. Lighthouses (www.us-lighthouses.com)