How to complete The Broken Sky main quest in Horizon Forbidden West

You’ll start The Broken Sky immediately after leaving GAIA if you choose to pursue the Aether AI first. This quest has the lowest level requirement of all the subordinate AI quests, but it’s also one of the lengthiest in Horizon Forbidden West. This guide explains how to complete the quest, including some tips for defeating the mammoth of a boss.

Step 1: Visit Aether’s coordinates

As you’d expect, this quest isn’t as simple as it might seem. The coordinates for Aether are the stronghold of one of the Tenakth tribes. When Aloy arrives, she’s surprised to hear that she’s expected. Follow Dekka through the museum and watch the holograms along the way if you want. You need to visit the tribe’s leader, who will tell Aloy that she can enter the room beneath his throne, where Aether is kept, if she helps him.

Step 2: Meet and follow Kotallo

Follow the quest marker to meet one of the last living Marshals. He’s been tasked with taking Aloy to a stronghold where a tribe’s leader has refused to send his warriors to a ceremony. Once you meet him, you’ll need to follow him along the road to the stronghold, a huge walled-in village. You’ll need to fight a few rebels along the way, or you can sneak past them if you’d prefer. Once you arrive, the leader sends you away. He won’t send his warriors while the wall he’s behind stands.

This gives Aloy an idea, and a new step in the quest appears. You need to head out of the village to a specific spot where you can look at the Bulwark. Scan it to find a tank, a potential weakness. You’ll need to climb up and into the wall by ascending the waterfall to your left and breaking in through a cavity. Inside, Aloy finds that she could destroy the wall with the right equipment.

Step 3: Take down the Tremortusk

The weapon Aloy needs is on a rebel Tremortusk, so you need to kill it to pick it up. Sneak around the area first, killing any rebels you can with silent attacks. Ensure you kill any rebels on towers before you alert the Tremortusk. The best way to get the drop on the Tremortusk is to use the Pullcaster to get up onto the walls next to it. Then, you can get a couple of good shots off before it starts to attack.

The Tremortusk is weak to frost damage, so use everything you have that deals it. There are a few containers of Chillwater and machine corpses with it in around the area, so shoot them when the Temortusk is near them to freeze it up. The underbelly of the Tremortusk is a substantial weak point that will explode into flames when burst. Shoot this at first, then aim for the ends of each tusk or the guns on its side. These weak points will deal more damage and build up frost faster.

Step 4: Destroy the Bulwark

After killing the Tremortusk, head back to the Bulwark. Aloy can then use the weapon to blow up a part of the Bulwark to reveal the tank and then cause the whole thing to collapse. This will complete the quest, and you’ll be able to head back to Aether, one step closer to getting it for GAIA.