Time Out says
In celebration of history and art (not to mention the Smithsonian’s free admission policy), over 1,300 museums around the country open their doors to the public free of charge. Visit family-friendly favorites like the Bartow-Pell Mansion Museum, the Dyckman Farmhouse, the New York City Fire Museum and the Cooper Hewitt, Smithsonian Design Museum. Head to smithsonianmag.com to see which institutions are participating this year and to download a free Museum Day Live ticket. All ages.