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Below is a walkthrough for the Level 30 side quest called Forbidden Legacy in Horizon Forbidden West. To obtain this quest, speak with Alva during the Gemini main quest after speaking with Beta.
Go to Legacy’s Landfall
Travel to Legacy’s Landfall, which is on the far western side of the map on the Isle of Spires. Call Alva at the Campfire.
Follow Alva to the Research Facility
Follow behind her until she stops at a beach!
Search the Ruins of the Data
As you approach the ruins, a giant machine will spawn.
Kill the Slitherfang
Defeat the machine!
Search the Ruins for the Data
After defeating the Slitherfang, continue your search of the ruins. Scan the ruins to find a vent that you can pull out. Interact with the vent to open it then proceed through the water. Make your way to the upper floors to find a Holo Projector and interact with it.
Follow Alva to the Atbay Headquarters
Follow behind her until you reach the ruins of a nearby building.
Find an Entrance to the Atbay Headquarters
Use your Pullcaster to pull out the wall near where Alva is standing then work your way up the shaft until you reach a window at the top. When Alva asks how you’re going to get across, use your Pullcaster to pull down a metal beam across the way. Head across it then shoot the ladder to cause it to drop. Sneak past the Glinthawks as you continue to make your way up.
Jump to the Tower
At the top, walk across the thin beam then pull out the debris and jump to the tower.
Search the Headquarters for Data on Leviathan
Scan the Passcode Reminder Reset Datapoint next to the door. There is another datapoint called Useless to the left of the door in the little nook. Use the code of 102023 to unlock the door. After just passing through the door, look on the right to find the AGI Log: 10/1/47 Datapoint. When the datapoint finishes playing, the door will unlock.
Climb up to the Ancestor’s Office
Continue making your way up to the top of the building to find the top of an elevator shaft. Ignite the Firegleam to send the elevator down to Alva. Afterwards, scan the Prototype Device, Award Statue, Sculpture and Construction Drone in the room. Use the code of 402625 to open the door. Interact with the Holo Projector to complete the quest.
Rewards
- 9750 XP
- 3 Skill Points
