This guide shows the complete walkthrough of “The Bristlebacks” side quest in Horizon Forbidden West. You get this quest by talking to Ulvund in Chancrape at the location shown in the picture below. After that, go and talk to Javad The Willing in the cavern nearby.
Search West of the Quarry for Bristlebacks
Go to the quarry. Walk n the path along the river and you will find the Bristleback Carcass near the waterfall at the location shown in the pictures below. Examine the carcass.
Follow the Trail to the Back of the Valley
Follow the trail and it will lead you to the mine as shown in the pictures below.
Investigate the Mine
Enter the mine and continue in the linear path. Eventually, you will come to an area with the collapsed old cart tracks. Enter the tunnel with the blue glowing plants on the right side of the track as shown in the picture below. Climb the wall at the end of the tunnel and you will reach an area with a few machines.
Investigate the Smoking Tunnel
Defeat the machines and enter the smoking tunnel on the west side as shown in the picture below.
After entering the smoking tunnel, turn left and you will find a pit full of barrels. Jump inside the pit and examine the note as shown in the pictures below. Then report back to Javad the Willing.
Find the Source of the Bristlebacks Beyond Barren Light
Finish the main quest 4, The Embassy, and this objective will be completed automatically.
Search North of Barren Light for the Rebel Camp
Go to the Rebel Camp at the location shown in the picture below. Enter the camp and defeat the rebels & their machines.
Investigate the Cave
After defeating the machines, climb up the ramp to reach the cave entrance as shown below. Here you will find a raised-up drawbridge.
Rotate the lever to the lower one-half of the drawbridge. Then shoot the two supports holding up the other half of the drawbridge as shown in the picture below. This will create a path to go inside the cave. A cutscene will start as you go inside the cave. Then report back to Javad the Willing to complete the quest.
