So, it's hip deep AND not quite wide enough for me to stand in sideways. But I finally caught the terrified little thing and got it out of the window well. The whole time, I was under the steely gaze of an adult robin, which stood on the front step next to the window well. In fact, it wasn't very far from from me at all. I am very grateful it wasn't the dive-bombing sort.
Once out of the window well, the robin made immediately for a tree and I noticed several other juvenile and at least one (I think at least two) adult robins in it. I guess I didn't know that robins are so faithful to the family unit even after fledging.