Lynnewood Hall is a 110-room palace outside Philadelphia, closed to the public for more than 80 years. It was built for the Widener family. A father and son, George and Harry, boarded the Titanic in 1912 and never came home. Inside were more than 2,000 artworks that later helped found the National Gallery of Art. This fall, for the first time in generations, the doors open. You can walk in.