Wanted to pass along this information from this Washington Post article
U.S. Botanic Garden: The display features trains running over 800 feet of track through miniature villages, mountains, drawbridges and more. 100 Maryland Avenue SW. Daily 10 a.m. to 5 p.m. (Tuesdays and Thursdays until 8 p.m.). Through January 5. Free.www.usbg.gov/exhibits.
Brookside Gardens: The South Conservatory is filled with trains, plants, buildings and a miniature ice rink. 1800 Glenallan Avenue, Wheaton. Daily 10 a.m. to 5 p.m. (Closed Christmas and New Year’s Day). Through January 5. Free.www.montgomeryparks.org/brookside.
The Ellipse: Toy trains run underneath the National Christmas Tree, behind the White House. The best entrance is at E and 17th streets NW. Daily from 10 a.m. to 10 p.m. through January 1. Free. thenationaltree.org.
Union Station: The annual toy train exhibit runs in the main hall with two trains, 200 feet of track, a village, mountains and a forest for the trains to run through. 50 Massachusetts Avenue NE. Monday-Saturday 10 a.m. to 7 p.m., Sunday 10 a.m. to 6 p.m. Through January 3. Free. www.unionstationdc.