Near the edge of the map, behind the rusted building with the hole in the ceiling and wall, across from the green 'tower' of alien tech; there is a cubed, fenced area with an open fence access gate, and a blue cube van 'parked' up against one side of the fence. This fence 'cage' has an open top, but the entire thing is covered in an invisible wall rendering it inaccessible. This can be used as a choke point against enemies since you have invisible walls to hide behind, and may stop the respawning of loot caches(chests).