This carriage house is located at 3324 18th Street, NW:
The listing says:
“Own DC’s most unique residence at The beautiful Schafer Mansion- The Carriage House. Offers the utmost in privacy and comfort. Features a lower main level and an upper level with 1bed/1 bath and private yard. View by appointment only.”
You can see more photos here.
This 1 bed/1 bath is going for $459,900 ($285 monthly fee.)