What was this book?

[little_farm_girl]

All I really remember is the boy fell through a hole in the ground, and I think he hit his head, and he saw a deer, and there might have been something about a key. Maybe the cover had a boy falling?
I'm pretty sure it wasn't The Fall by Garth Nix.

[Craft Forums]

[little_farm_girl]

Ok, I found it.
The Forgotten Door by Alexander Key.