Get into the building on the left. You'll Get attacked by drones - finish them off hiding behind vehicle wrecks. (if the fight still continues even though you seem to have killed all enemies, check if there are no more left under the bridge). Get into the building and go downstairs. In the slums under the bridge, you'll get attacked by wretches - shotgun comes in handy here. Near debris pile kick the door in and enter the building. Walk through the corridors and go outside on the other side of the building. Now you can pick door ahead or to your left. Pick the left to reach Troika gun and use it to eliminate drones downstairs. Looking out for survivors go through the window.
You will find yourself in a well-defended park. There is a gun there but it's not that dangerous as you have quite a number of barriers to hide behind. Try to kill as many drones near the gun, as it's possible, flank the rest from the left and wait for Boomers. On your left there should be a sniper gun so getting rid of them shouldn't pose a problem. Keep the gun. Take the ammo and walk through the door you saw the Boomers come in. Eventually, you'll reach another park, killing drones again. Pacify them with you sniper gun. After that you'll visit slums again. After taking care of the wretches, finish off two drones in the park and the one hiding behind the small building. Use the valve. After you enter the garden, take a little detour and go left. In a small alley you will find ammo and 28.Tag.
You'll be attacked by drones. Defend yourself using sniper gun or lancer, depending on the situation, until Brumak comes. Now you can choose the way. I suggest going to the gallery. Finish off snipers from inside the room - trust me it's a better way than hiding behind the barriers. Then get rid of the gun crew below. After that proceed to your main task - destroying the round attachments over the monsters head. Sniper gun should do the trick here. Immediately after that you'll get attacked by wretches, so get ready and take appropriate position. Kill the rest of the snipers and when a door opens get to the other side.