The quarry is half surrounded by high cliffs with narrow entrances in the northeast and southeast corners. Approaching from the west allows you to survey the area from the high vantage point and then stealthily descend into the base. If you are on the southeast side, look for a Parkour Up device to reach the path above, which takes you to this same point. This also puts you close to the commander and two treasures. One captain roams the outside on the ground level, while the second guy is typically just inside the opening at the base of the western side. For the third treasure, spot the higher of the two cranes and then access the small room below it. Enter the opening at the base of the west wall, move around the limestone blocks, and bust through the wood door to find the final treasure inside another small room.