"Cult of the Vault" is a challenge from Tiny Tina's Assault on Dragon Keep DLC
The full title of these docks is : Unassuming Docks of Potentially Little Importance
The First symbol is found in the Forlorn Ruins in the Northeastern part of the docks. Look for the little stone shed. Go to its eastern side to find it. The location is marked on the map.
The Second Symbol is found in the Hamlet of Swift Passing Through. Head for the entrance to Flamerock Refuge then go on up the stairs toward the house. Head on over to the far Western side of this area. Under the overhang you can find at the far Western end you will find the SYmbol.
The Third Symbol is found The Unrelatively Unvisited Shoreline. Head along the beach's edge until you find an archway. The top left of it will be damaged but the arch itself is intact. Head around the right-hand side of it and look behind there to find the Symbol.
Ranks and Rewards
Badass Ranks: 5