Photo courtesy of Library of Congress. Ever walked from the Foggy Bottom Metro stop down to the Mall? You’ve likely walked down 23rd Street and noticed a highly fortified complex near E Street, owned by the Navy. what you’re walking by is the Potomac Annex, also known as the Old Naval Observatory. Located on Reservation 4 of the L’Enfant Plan for the Federal City, George Washington chose the site for a university, but it…