The Avant Gardens Out of Bounds (OOB) area is a, well, "area" that's out of the boundary of the map. Before jetpacks came out, the only known way to get there was a very difficult set of jumps on a specific area of the map.
Once there, it is possible to glitch your way to the top of the map where you appear to be "floating" above Avant Gardens.
Members of the F.2.P.A.G.P. visited it once in a while or try to. Some even tried to sell tours of the area (No one would buy :( ). Most of the time, they would just run around in it for no reason at all.