Avery's Descent is the nineteenth chapter in Uncharted 4: A Thief's End.
Plot[]
Nate and Elena descend the stairs and pass through a metal gate which shuts behind them, barring any backtracking. They find themselves in a tunnel system Avery used for secretly bringing his treasure to his ship. In the tunnels, they find body parts of pirates killed by Avery, and mummies that explode if someone comes near them. Several death traps have to be overcome.
In the hand of a skeleton, Nate finds a key. When they come to a locked door, they hesitate to use the key because there might be a trap. When they eventually open the door, they are caught in a net. Nate succeeds in recovering a sword from a dead pirate, and he cuts the net. They run to the exit of the tunnel system, passing more exploding mummies.