This is the doorway leading to what I think was an abandoned pool or something similar on the Copeland Estate. The Copeland Family was a branch off Delaware's prominent DuPont family. Although the door lead to an abandoned pool, it reminded me of the book The Secret Garden in which the main character Mary discovers a door covered in weeds that leads to a secret garden. I imagined that this doorway was like the one in the book in that it led to a secret garden.