Youre a member of the Deadwatch.
The Deadwatch stumbled across a dungeon thousands of years ago, a collection of ancient ruins and catacombs, that seems to change every time you enter it. Most of the rooms are the same, but the order is different. Doors you remember being open are closed, and doors never open are now so. No one really knows why this dungeon exists. It senses your strength and adjusts the difficulty to make each encounter harder.
With its purpose long lost to time, all that the Deadwatch use this dungeon for is to rank each other. Compete against other players around the world to reach deeper into the dungeon than anyone has before.