DOOM 2016 – The third secret room
Once before you open the heavy gate, turn left. You will see a blue door, follow it across the bridge.
At the door to the fork, you need to go to the right side.
Stay at the bridge, you will see that in the middle of the crossing with a small platform.
On the edge of the platform is a lever that you want to rotate.
Look into the distance, you will see that opened the door in the wall. You reach it by climbing over the bridge.