Sugar Shack

enter the the hole and take the left, go up the stairs and down the railing some, on your right will be another railing walk way, take it towards the hole and hop over the debree, hit the power switch you see and it opens the door.

Inside you will complete the challenge and find the 2 pictures of Moxxi from Borderlands 1, Mad Moxxis Inder Dome, some pizza, some panties, and a stick with Moxxis hat...