Mount Vernon's Secret Treasure

I'm a fan of the National Treasure movies, although (or maybe because) they require a hefty suspension of disbelief to accept the notion of buried loot in lower Manhattan or a city of gold underneath Mount Rushmore. So imagine my surprise when I read in the Washington Post's "Reliable Source" column today that the films aren't entirely fictitious. "Damned if Mount Vernon doesn't actually turn out to have [a] super-mysterious secret basement!" write Amy Argetsinger and Roxanne Roberts. And now the overseers of George Washington's home have decided to open the basement to the public. But curious sightseers won't see the secret tunnel leading out of it that's depicted in the movie. That's made up.