This area is reachable.
After you pass under the remains of that bridge (walking from the side of Three Horns and Fink's, from a road with derelict cars), there is an entrance on your right. When you first enter the Fridge, the mission takes you left, down the road towards the Highlands, so most people overlook this way. The entrance leads into a series of rooms, one of which opens to the bridge above, and one can leap across to the area you see.
If I recall correctly, these rooms are always accessible. In case I'm mistaken, though, there is a mission that requires one to pass through them, Swallowed Whole, that is unlocked after completing the Rising Action main mission.