Rainy Day in Washington, DC
Enjoy live theater, a concert, or a dance party (tip: catch Broadway shows at National Theatre, don't sleep on Ford's Theatre, Studio Theatre, Arena Stage, or Atlas Performing Arts Center) (tip x 2: dance parties are often at Union Stage, Black Cat, and Songbyrd)
Watch a movie (tip: try local theaters like Landmark E Street Cinema, Suns Cinema, or AFI Silver for more unique showings)
Go to the National Zoo (argument: seems counter intuitive, but there's so many 'Houses' and usually animals are inside when it's raining)
Cozy up at a bar & find a warm meal (tip: a Belgian beer and mussels at Granville Moore's always does it for me)
Play a board game (tip: head to Labyrinth or Board Room) or do an indoor activity like mini-golf or ping pong (tip: Swingers or SPIN) or bowling (tip: Pinstripes or The Eleanor) go rock climbing (D.C. Bouldering Project or Movement Climbing)
Visit nature inside at the U.S. Botanic Gardens (tip: great spot to read a book)
Explore a museum (tip: National Portrait Gallery, National Building Museum, Textile Museum, and Phillips Collection are great for different exhibits/ rooms/ architecture + not too cramped)