Stairs forged in stone and unnatural stone formations suggest that you're closer and closer to the centre of the Locust territory. At the foot of the formation you will have to fight some enemies. You will meet a Kantus for the first time. Use the Rockworms to get closer to the enemy.
Right past the gate, on the right you will find a Locust Emblem lying on the floor. After crossing the room you will have to choose - go left or right.
Don't waste ammo; use the Rockworm to flank the Troika. Just hide behind his body and patiently follow it. When it reaches the end, dispose of the two Locusts who were using the guns.
Pull the lever and enter the newly opened gate. You will reach a place below which another team is fighting a group of Locust commanded by a Kantus. Help them by shooting enemies from above.
Shoot the shiny fruit to lure out the Rockworm. And to be precise its three fruits thanks to which the team below will be able to cover behind the beast.
After shooting the last fruit you will be attacked by Wretches. Kill all of them and activate the lever coming out of the floor. Go through the door. During the road to the next post you will attack from below while hiding behind Rockworms and Dom with Carmine will attack from above. After killing the Kantus and the other defenders, Boomers will appear. You can use the Troika mounted next to the gate to get rid of them.