"Cult of the Vault" is a challenge from Tiny Tina's Assault on Dragon Keep DLC
The First symbol is found in Wailer Drop. This one is easiest to get AFTER you have completed the story inside the Lair of Infinite Agony. Enter into the Lair, head over to the first elevator, that takes you to the second level of Wailer Drop. go to the Northern end and jump, carefully to the alcove below in that Northern wall. This is also where you found Crumpet 1, if that makes things easier.
The Second Symbol is found in the Chamber of Woe. You need to make it to the room with the trapped floor, the crushing floor part of it. Cross the crushing floor and deactivate it. Once you have head back into the hallway and look along the Northern Wall in the far-left set of bars. On the right-hand side of it you will find the Second Symbol.
The Third Symbol is found in the Hall of the Dead. Access it through either Wailer Drop from the South or come in from the West through the Bone Barracks. Head to the Southern edge of the opening down to Death Quencher Well. Go to the Eastern side and jump down to the balcony you can see below you on the right. Look on the floor of the balcony to find the final Cult Symbol here.
Ranks and Rewards
Badass Ranks: 5