|Kill 2 enemies with one Railgun Slug shot through a wall|
Wall Hack is an Achievement/Trophy in RAGE. This Achievement/Trophy can be earned by killing two enemies by using the Railgun Slug ammo type, shooting through a wall. Note that this can only be earned after downloading RAGE: The Scorchers.
The place that tends to have many enemies bundled together behind walls would be the Wasted Garage. Finish the quest "Rumbles in the Dark" as soon as possible to have access to the Nail Gun when completing the quest "Find the Buggy Parts".