About 90 museums that are participating have a partnership with the Smithsonian Institution to show artifacts on loan from the museums in Washington.
Museum Day runs all day Saturday.
In Baltimore, visitors can see George Washington's false teeth at the National Museum of Dentistry. An entire gallery is devoted to the first president's dental health. The teeth are on loan from the National Museum of American History.
At the U.S. Space and Rocket Center in Alabama, visitors can see a Saturn V rocket.
More participating sites can be found on the Museum Day website.
Visitors must print a free admission card from the site that admits two people.