Come explore the Fort and discover this treasure of Maine and United States History. Fort Knox is open May 1 – October 31, from 9:00 – sunset. The grounds are open year round for your visiting pleasure. The newly constructed Penobscot Narrows Bridge boasts an observation tower, rising 420’ above sea level, which may only be accessed through the Fort. The observation tower provides a breathtaking view of the Penobscot River Valley, and is the only observatory like it in the Western Hemisphere!