US Naval Observatory Administration Building

From www.usno.navy.mil:

...by the 1890's, it was clear that the Naval Observatory had to move out of the city. Unhealthy conditions in the Foggy Bottom neighborhood had taken their toll. In 1893, after nearly 50 years at the site on the Potomac River, the U.S. Naval Observatory moved to its present location. At that time, this rural site was well outside the city in the countryside above Georgetown. The move not only provided better astronomical observing conditions, but also provided an opportunity to rethink old scientific programs and propose new ones. Along with the new programs such as daily monitoring of solar activity, the old functions of time keeping and telescopic observations were kept intact when the Observatory moved to the new site. The old Observatory in Foggy Bottom was declared a National Historic landmark in 1966.