What an awesome photo from the Civil War era. You’re looking up what is Independence Ave. today.
In this image, the central roof of the Castle is intact and the small towers have the caps on them. In January of 1865, a fire destroyed the central roof and the caps on the towers, so this photograph had to have been taken prior to January 1865 and is most likely April 1863. The Capitol dome, seen in the distance, is not yet completed