The Blueberry's first trip to the zoo was very brief--we got there about an hour before closing and it was cold. He did stay awake for our entire visit, which surprised me, looking all around. However, from his vantage point he probably couldn't see much other than the trees and me, of course. Next time we go to a zoo, the Blueberry will likely be mobile or at least ready for a forward-facing seat in his stroller.
The highlight of the visit for my friend's son was the playground. It's a very cute jungle gym laid out in the shape of a train. The Blueberry wasn't particularly impressed, but he no doubt will be as soon as he can walk.