The images above showcase the exclusive Shanty Town Multiplayer Map you will receive as the final pre-order bonus for Tomb Raider. This area has been built up by the scavengers on the island and features many steep climbs, zip lines and traps to maneuver. It looks as though, at least in the US, you will receive this bonus when pre-ordering from any retailer. This includes Amazon, Gamestop, Best Buy and Walmart.
Note: This DLC map was previously referred to as the "Endurance Pack" in earlier stages when multiplayer was yet-to-be announced.
Source: Official Tomb Raider Blog
