The grand capital on the Potomac has plenty of wonderful museums where you can spend days roaming around and not pay a cent. Given its importance, security is tight everywhere so be patient with the checks and pack light to help you get through everything quickly.
The capital was established in 1790 by Congress to create a home for the federal government. The layout was planned by Pierre Charles L'Enfant, a French army engineer who designed broad diagonal avenues and a grid of streets. However, the city had declined in the latter half of the 20th century due to suburban flight, although the tide is changing with a younger demographic moving back in to revitalize urban neighbourhoods.
In 2016, 22 million visitors came to DC, with the 3 most visited attractions being the Lincoln Memorial, National Air and Space Museum, and the National Museum of Natural History. That's a large number given the population is just over 680,000 people.