Not even the geocachers know where it is.
Number of people there when I was there: 13
Located halfway up a steep hill, completely cut off from most conventional forms of transportation, sits one of the coolest museums I've seen in DC. What the Anacostia Community Museum lacks in access it makes up for in personality and local information.
There's a whole section dedicated to "blockbusting" and segregation in DC, another with maps of the first settlements in Anacostia, and a third showcasing some of the families that were long-time residents. Most museums tend to have a sort of sterile or austere view of the artifacts they keep, and don't give an impression of change over time. The thing I really like about the Anacostia Museum is not only that their collection of narratives is (by it's nature) both engaging and historic, but also that it's set up in chronological order and has a whole section on future plans for neighborhood development, including the 14th Street & Good Hope Rd. beautification effort and the plans for the I-295 pedestrian bridge. The museum also pays close attention to Anacostia community leaders, and the issues they faced during their time. That's the sort of information you won't get anywhere else, and to me epitomizes why museums were created to begin with.
I don't know why they put the museum in the middle of nowhere without good signs or an easy entrance (it's at 1901 Fort Place SE, 20020 for those who like google maps):
If you have a couple free minutes some day between 10am and 5pm, even on Sundays, you should go. The people were even really polite (nay, kind!) when telling me I couldn't take pictures inside.