Gears of War 3 - Unbreakable

Turn around. On the wall just a little to the right is a silver plaque. Check it out because it's a collectable.

Head up the stairs on the right and continue on the snaking catwalk. Eventually, you'll come to a large room on the right side with a painting on the wall. The Painting is a collectable. And if you continue further along the catwalk, you'll come to a small ammo room (directly ahead) and in the left corner is a pile of medals, this is also a collectable.

Load up on ammo and just make your way up the ramparts to the Gate of Anvil gate. I would actually recommend crossing the gate over to the right side. Jump on the turret and start blasting away. Keep tearing through enemies until eventually a catapult will show up. After a couple of shots, it will take down the main gate and you'll have to fall back to the main court yard. Most of your allies will assemble at the catwalk so if you just move back just a little you will find a small area that sticks out. This is a perfect flanking spot. Just keep hammering the enemies in the court yard and they'll likely pay little to no attention to you. If you need ammo, there is a full box if you go back to the ramparts and some more closely to the catwalk.

When the Maulers arrive, there's actually a OneShot at the ammo cache near the catwalk. Grab that and use it to take them out. A perfect reload will actually pack enough punch to destroy even the Mauler shields. Eventually you'll have to retreat further. If you follow the path they give you, there is a turret at the very end to use. The grubs will start trying to use their grappling hooks to climb up and you can shoot these off just like in Gears 2. They are a little tough to target however since they actually attach to and clip through the ground a little.

The final phase takes place when the Boomers blast through the doors to the garage. From there, just hold them off until they tell you about the "Last resort" and when they tell you to, focus your fire just behind the grubs.