The amazing thing with this gorilla exhibit, besides the fact that in 1979 it opened as the very first naturalistic gorilla enclousure on the planet, is that visitors have no clue as to where the habitat ends. Where are the fences, bars or moats? I have no definitive answer, and I almost expect to see a gorilla run into the background and never come back. The zoo uses the treeline to naturally obscure any kind of hidden barriers, and the same effect is brilliantly utilized for the grizzly bear, arctic wolf, rocky mountain goat and river otter enclosures in the Northern Trail section of the zoo.