I really dig it, and I love that it has a sort of older-times, action-adventure feel. I agree with Toby that the person seems a bit over-exposed, as he's presented here*. What if he was lying on his side, with one leg kind of drawn up, and he was lifting his head up just a bit to peek through a gap in the broken rock of the ledge's rim? When my cats are lying down while playing (seems an oxymoron, but cat owners should understand), they often keep one of their back legs bent, tensed, and with their claws dug into the carpet so they can spring away in a moment. Perhaps if this was a bit less static; just something to show that there is the potential for danger, in his spying.
The book is fantastic, and I'm really happy it might be published soon.
* unless the scale is off a bit here, and in the final drawing the person and the thing he is observing are a very great distance apart, so that his being exposed isn't a big deal. I should remember, having read the book, but my memory is terrible.