The claim that the Wall is 300 miles long is further supported in Game of Thrones: A Telltale Games Series, where Britt Warrick says to Gared Tuttle a 300-mile wall, and you're still in my way. The game is canon to the show so it is possible that Sam was wrong.
One of the most respected collections of museums in the world, the Smithsonian Institute is an inspiring attraction for kids, teens and adults. Comprised of 19 different museums, art galleries and research centers, the Smithsonian collection is centered around the National Mall - and admission is always free. The most popular Smithsonian museums include the National Archives, National Zoo, National Museum of Natural History and the National Air and Space Museum.
Don't miss the other Smithsonian Museums that are located off of the Mall: National Zoo - Rock Creek Park, Washington, DC. The National Zoo is a part of the Smithsonian Institution with more than 435 different species of animals.