When we travel in The Fridge area, near the exit point to The Highlands Outwash, we may encounter a Goliath; and if we manage to kill him before he transforms, he will drop an ECHO recorder that has an optional mission for us, known as Borderlands 2 Note for Self-Person.
By listening to the recording, we find out that the Goliath ordered some weapons from Marcus Kincaid, but the weapon cache has been delivered to his brother, so we need to find that cache, killing some midgets in the process.
"A Goliath named Crank has a cache of weapons hidden somewhere in The Fridge. Go find it.
Item: Rocket Launcher
Experience: 3859 XP
For the Borderlands 2 Note for Self-Person mission we need to go to The Fridge's entrance, near the exit point to Three Horns Valley (through the door that was used by Laney to come out in The Cold Shoulder optional mission). We go inside the Rat Maze region and we kill the rat enemies we find, preferably from a safe distance, one at a time.
By the time we reach the cache's location in Crystal Claw Pit, we should've already completed the secondary objective by killing ten midgets (we can always go back if we don't find enough of them and we want to complete the secondary objective).
When the area is cleared, we shoot the ice surrounding the cache in order to free it. Then, we turn in the mission by opening the weapon cache. However, by doing this we will also free the frozen enemy from behind, a boss named Smash Head. His attacks can kill us in an instant, so a good strategy here is to equip a rocket launcher immediately. If it happens to kill us, we can always shoot the midgets who climb on Smash Heads back to attack him, in order to get a second wind.
Once Smash Head is dead we can turn in the Borderlands 2 Note for Self-Person mission to Scooter in Sanctuary, and then focus on other missions featured in The Fridge zone, or other regions.