History buffs have another reason to head to Mount Vernon in the next few weekends: The cellar where Nicolas Cage kidnaps the president in "National Treasure: Book of Secrets" is open for the curious to inspect.

The decision to open the basement to public tours was made when Mount Vernon staffers saw the movie. "When we saw what a pivotal scene it was, we knew the public would want to know about the secret tunnel," said Emily Coleman Dibella, Mount Vernon's director of public affairs. "For those of us who love history so much, it's great to see it up on the big screen in such an exciting way."

The decision was a popular one, with visitor numbers this past weekend up nearly 300 percent over a typical second weekend in January, Dibella said. If interest remains high, the basement might be opened to the public again. For now it will be open for the next four weekends.

Alas, don't expect to find any cornerstone-triggered secret doors revealing labyrinthine tunnels. The tour guides assure visitors that the network of secret passageways in the movie is pure Hollywood invention.

But as you descend the steep steps leading into the tunnel-like cellar, it's easy to see where screenwriters got the idea. The cellar has never been open extensively to the public, in part because its walls are slightly crumbling.

It originally was used as a dining area for servants and slaves (look to your left as you enter the basement) and for storing food and alcohol and ice in the arched storage areas on your right. Ice, hauled in from the Potomac River, also was stored in the cellar.

Visitors walk about 40 feet through cramped quarters to the mansion's cornerstone, which plays an important role in the movie. The stone that visitors see in the basement is a replica of the original, which is in Mount Vernon's new museum.

Movie fans will notice that the initials in the real cornerstone are "LW," for Lawrence Washington — George's half-brother and original owner of Mount Vernon. This bit of history was too much for Hollywood, so for the movie, a new cornerstone was created with the initials "GW."

Despite the mixing of fact and fiction in the movie, visitors on the first weekend the basement was open were thrilled with their good fortune.

Patricia Huie, her husband, John, and their five children were visiting from Alabama and hadn't realized that the basement wasn't normally part of the tour. "It's really exciting," she said.

If you go to Mt. Vernon

MOUNT VERNON, at the end of the George Washington Memorial Parkway, about eight miles south of Alexandria, Va.

Contact: 703-780-2000 or www.mountvernon.org.

HOURS: Basement is open weekends from 9 to 4 through Feb. 10. (The basement is also open during the twice-yearly wine festival, but that tour is less extensive.)

ADMISSION: $13 for adults; $6 for children ages 6-11; free for 5 and younger. Includes a tour of the mansion and movies and displays at the visitors and education centers.