First of all, you need to return the same way that you took earlier, in to the surface. So, start by lifting the hatch, thanks to which you will be back near the Derelict Elevator Shaft. Go West [Burnley Sewers - East], and listen to the radio communication on the radio, which concerns the gang war, which is connected with Bird's side mission (you can find its description in a separate section of this guide). Return to the main part of the Burnley Sewers and use the hook to return to the ledge in a considerable distance above. Select the glue grenade from the inventory and seal both pipes. Go West and use the hatch, thanks to which you will return to the Burnley district.
You can now go to the western part of the Park Row district, because that's where Bane's tracker is leading. Approach the destination from the North-Eastern side, deal with the sniper shown in the screenshot, who is occupying the rooftop of one of the taller buildings around.
This is not the end yet, because directly above the mission's objective, there is another sniper. It is worthwhile to glide towards that bandit, land behind his back and perform the quiet takedown. While you are still here, deal with the enemy patrolling the nearby walls also, and keep necessary precautions, because he is also equipped with a firearm.
Try now to reach one of the small balconies to the East of your destination. Thanks to this, you will notice that the tunnel's entrance is guarded by several bandits. Glide towards the enemy with the gun, knock him down and finish him off. Only then, take to the remaining enemies, who should not obstruct you from performing your mission anymore.
Do not attempt to look around for the locator in the spot marked by the game, because you first need to reach the sewers. Enter the blocked off tunnel, turn right and locate the door shown in the screenshot. Climb down the stairs and unlock the access to the venting shaft, which will take you to the sewers under the Park Row district [Park Row - Sewers Access]. Jump onto the balustrade and surprise the enemies directly in front of Batman with an explosive present. Only then, jump down and start fighting, while minding the enemy with a shield and the enemy wearing the heavy armor. Apart from that, do not allow the remaining enemies to start firing at you, and remember that using the shock gloves will considerably help you win this one.
After you have won all the fights, locate the weakened wall fragment and spread the explosive gel over it. Approach the water reservoir [Park Row - Sewers], select the glue grenade from the inventory and target it at the water (the screenshot), which will result in the creation of a floating platform. Jump onto the raft and use the claw on successive anchor points, which will allow you to reach the other end of the reservoir.
The attempt to open the door will equal starting new fights with Bane's men. You need to watch out in here even more, because you will bump into two heavily armored enemies. At first, avoid fighting them (you can stop them using the glue grenades), and focus on the standard enemies, and on the enemy with shield. Attack the strongest enemies only after the shock gloves have fully charged, which will make them die quite quickly and not threaten Batman too much.
[New Character Trophy: Mercenary]
Take the entrance to Bane's HQ [Bane's Field HQ - Entrance], walk down the stairs and unlock the armored door. After you reach the main area in the HQ, the game will display a cutscene, during which your character will learn and important thing.
[New Character Trophy: Bruce Wayne]