Most zoos take great care of their animals in an effort to aid conservation.
There are of course examples of places where the size of the pens is insufficient, and in the wake of documentaries like "Blackfish," more and more of these locations are being shut down.
Even at zoos where animals are well cared for, there's always the chance of escape. For one hippo in Israel, an open gate was the chance of a lifetime to taste freedom. But what she decided to do in the end shows there's no place like home.