How to get to Murderlin's Temple (Tiny Tina's Assault on Dragon Keep: A Wonderlands One-Shot Adventure)
Murderlin's Temple is home to the arena in Tiny Tina's Assault on Dragon Keep: A Wonderlands One-Shot Adventure, and it's a great place to farm XP after completing the game in True Vault Hunter Mode, and one of the most efficient places to grind to level 35.
To find Murderlin's Temple, you need the quest "Find Murderlin's Temple" that you can accept from Moxxi in Flamerock Refuge after completing the main story. Accepting this side-quest spawns the gate to enter Murderlin's Temple from Flamerock Refuge.
The door to Murderlin's Temple is always there, but you won't be able to travel to it until you have accepted the quest. Since you need to beat the main story line to get the quest, this area is considered one of the end-game features of the game / DLC.