Built in 1766 in what was then the British colony of Maryland, the capital's oldest surviving building has been a tavern, a brothel and a boardinghouse (sometimes all at once). Today it's a small museum offering a peek into Revolutionary War–era life. The evocative little garden out the back is worth a mosey. Check the website before visiting, as the upper floors of the extensively renovated house were yet to open at the time of research.
It was almost demolished in the 1950s, but a persistent (albeit false) rumor that George Washington and Pierre L’Enfant stayed here while surveying the new capital of DC saved it for posterity.