Things to do in Washington DC

5 hours by car depending on traffic; domestic flights exist but rarely save time once airport transfers on both ends are counted. Many of the city's biggest draws cost nothing: most Smithsonian museums, the Lincoln Memorial, and the Capitol (a free guided tour, but one that needs booking in advance). The Washington Metro runs on its own farecard system, separate from New York's OMNY.

A single day covers the essentials, but two days are needed to walk the National Mall properly and spend real time inside one or two museums. With 3 hours of train travel each way, a same-day round trip leaves only about 4 to 5 usable hours in the city, so an overnight stay is the more realistic way to see it.