WASHINGTON D.C. Dumbarton Oaks, in Georgetown, the house was bought by Robert Woods & Mildred Barnes Bliss in 1920 & filled with their collection of Byzantine art. In 1963, Philip Johnson added a wing for their Pre-Columbian art. Go for the art, but stick around for the gardens. Originally designed by Beatrix Farrand, the original 53 acres have been split up a bit, but 27 acres remain as a public park and it is gorgeous from every corner and path and vista, especially at cherry blossom time.
The Pope-Leighy house was commissioned in 1939, by Loren Pope who was a copy editor for a Washington, DC newspaper, and earned fifty dollars a week. Pope wrote Frank Lloyd Wright a convincing letter persuading Wright to take on the project.