An nifty little Easter Egg I found in the Caustic Caverns. I congratulate Gearbox for their good taste in games, too. But, as you can see, this is a tribute to Dark Souls. It is pretty difficult to get to (understandably), and there is nothing there for you when you do.
Hung around for another half-hour after taking this video, trying to see if there were a puzzle or something. If there is, it's very, very clever; there are no signs on how to complete the puzzle at all (if there is one).