Prepositions – Difference Between ‘Slip Out of’ and ‘Slip Off’

"To look at [some thing]" means to specifically pay attention to that thing.

"To look to [some thing]" has various meanings, but in this context it means to look in the direction of that thing.

So if I say I'm looking at the parking lot, I mean that the parking lot itself is my focus. However if I just look to the parking lot, I'm just looking over toward that area with no special focus.

Similarly:

She's looking at the sky (There's something in the sky that has attracted her interest)

She's looking to the sky (She's looking generally upwards with no particular focus)

As a side note, to look to a person has a different meaning, "to hope or expect to get help, advice, etc. from someone":

I look to you to take care of the kids while I'm away.

Mary looks to Tom to cook their meals since she's been sick.

Edit: In a recent comment I wrote:

".. traders who deal in Netflix stock primarily look to subscriber statistics to determine whether they will buy or sell."

I used to rather than at, partly because I was still thinking about this question, but also to imply that the statistics aren't the only thing the traders look at -- they look at the statistics and other related data.

I don't find We went upon the hill particularly idiomatic. Upon usually describes a position rather than movement. It's far more natural to say

We went up the hill

but you can say

We stood upon the summit of the hill, admiring the view.