Dumbarton Oaks is a 19th-century mansion in Georgetown. It was one of the points of interest that we have checked out when we opted to visit the neighbourhood. I've been to Georgetown a decade ago, but there were nevertheless areas that I haven't checked out, such as this mansion museum.
The museum features artworks from pre-Columbian and Byzantine periods. It's not the most coherent collection, perhaps, but I suppose it works. It also has a music room that has a very elaborately painted ceiling. In 1944, this room actually was the setting for the decision to create the United Nations.
I must say I have been to other museums that are more eye-catching and breath-taking. But if you're in the area, then this is worth checking out. The collections are free, but you have to pay to enter the gardens.