Borderlands/The Back Door

The Back Door is a tunnel that connects the Salt Flats to the Crimson Fastness.

Arena Battle
When you see the two crates and ammo vending machine, you are approaching the final arena for this map.

There are three Crimson Lance soldiers, one equipped with the 10011 Cannon.

Weapon Crates

 * One at the mid-way point.
 * Two just before the arena battle.