HA-20-1922 is the name of one of the first aerial photographs taken over Ottawa in 1922. It was nearly lost to time. A keen historian uncovered this photo along with others taken from a "Flying Boat." You can read their story here.
http://history.ottawaeast.ca/HTML%20Documents/Airphoto_Study/1922/Earliest%20Air%20Photograph.htm
This cache is hidden a stones throw from the Old Ottawa East City hall. Just by the 417 Highway which follows the path of the old train tracks. If you look closely in the photo you can find the tracks and see a steam train running along them.