This is the General Noble Redwood Tree House and it used to be on the National Mall between 12th and 14th Streets, SW.
This photograph was taken around 1920 and until I saw this photograph, I had no idea that D.C. ever had a treehouse.
Apparently, the tree was placed in Washington to promote the 1893 World's Colombian Exposition in Chicago.
The tree was shipped in from California, where it took 20 men 7 days to cut it down.
This Redwood was massive and had a 26 foot diameter.
The treehouse remained on the Mall until 1932, when it was moved to Arlington and eventually burned.
Kind of sad, I wish it was still there!