https://www.smithsonianmag.com/museu...seum-day-2019/

Museum Day is an annual celebration of boundless curiosity hosted by Smithsonian magazine. Participating museums and cultural institutions across the country provide free entry to anyone presenting a Museum Day ticket. The Museum Day ticket provides free admission for two people on Saturday, September 21, 2019.
Tickets will be available to download on August 15, 2019.