There are a lot of side quests and errands in Horizon Forbidden West, and while most do a pretty good job of adding a little extra depth to the game's world, some of them can be fairly forgettable. This definitely isn't the case when it comes to the Forbidden Legacy side quest though, which is handed out by Alva towards the end of the main story.
The quest features a little bit of everything, from combat to climbing, with a few door code-related puzzles thrown in there as well. It's also one of only ten side quests and errands that actually need to be tackled to unlock the platinum trophy for Horizon Forbidden West, with the "Recovered Alva's Data" trophy being one of several rewards that players get for completing the quest.
How to Unlock Forbidden Legacy
Players will gain access to the Forbidden Legacy side quest near the beginning of the Gemini main story mission. After speaking with Beta down in the server room, players should head back upstairs and talk to Alva. They'll need to select the "Did you need help with something?" option, which will lead to Alva telling Aloy about a lost flood control system known as Leviathan. She'll then ask for help tracking it down and Forbidden Legacy will be added to the list of side quests in the player's notebook.
How to Find the Research Facility
To get the ball rolling, players should head on over to the Legacy's Landfall area, which is in the ruins of old San Francisco to the far west. Once there, they'll be able to call Alva from the nearby campsite, and, after a short conversation with one of the other Quen, she'll lead Aloy to some nearby ruins. Investigating the area a little will lead to a Slitherfang appearing from the sand, which players should dispatch using Fire, Frost, or Plasma ammo.
With the Slitherfang taken care of, players should look for a vent panel on the side of one of the buildings. Rather than using the Pullcaster to open it up though, they'll simply need to approach it and press the Triangle button to have Aloy kick it open. Heading to the upper area of this structure will reveal a Holo Projector, which, in turn, guides Aloy and Alva to the former headquarters of a company called Atbay.
How to Get Inside the Old Atbay Headquarters
After reviewing the data provided by the Holo Projector, Alva will lead Aloy to the nearby Atbay building. From here, it's up to players to figure out how to get inside, and they'll need to start by removing the blue metal frame from the nearby wall using the Pullcaster. They'll then have to climb up one of the building's interior walls using the yellow pegs and bars until they arrive back outside.
In this next area, there'll be a large beam that players can pull down using the Pullcaster and a ladder that can be shot down with a well-placed arrow. Crossing this beam and climbing the ladder will lead to a new area with a couple of nesting Glinthawks, which players will either need to kill. Once they're out of the way, players can continue their ascent, which will eventually lead them to a mass of debris with two removable metal beams sticking out of it.
What is the First Atbay Door Code in the Forbidden Legacy Side Quest?
Removing the beams with the Pullcaster will grant players access to one of the upper floors of the old Atbay HQ. They'll initially find themselves in a lobby-like area with a locked door and a Datapoint titled "Useless." Reading the latter will reveal that the code for the door is the month and year in which Atbay was founded, which Alva helpfully points out was October 2023. With this in mind, players should be able to deduce that the first door code is 102023.
After scanning another Datapoint in the next room, players should continue through the next door until they reach another dead end. Here, they'll have to remove the blue metal frame from the crumbling wall using the Pullcaster and then return to climbing the exterior of the building. There are a few more things that need to be pulled down on the way up, but, for the most part, the ascent is all fairly straightforward.
Eventually, players will find themselves back inside, where they'll find some Firegleam on the side of an old elevator shaft. Destroying the Firegleam crystal with the Igniter will cause the elevator to fall back down to the floor that Alva is on; clearing the debris and allowing her to climb up. Players should also head into the now-unblocked shaft and climb to the building's highest floor.
What is the Second Atbay Door Code in the Forbidden Legacy Side Quest?
Aloy and Alva are now agonizingly close to Eileen Sasaki's office and the data that Alva so desperately craves, but there's one final thing standing in their way. The locked door requires a six-digit passcode, but there are no Datapoints around to help players out this time. There are, however, some artifacts on the other side of the room, which players should head over and examine.
With the help of Alva, players will learn that these items are, from left to right, a trophy that Eileen won when she was 40, a water purification device called the H2Flow, a sculpture designed to celebrate the company's 25th anniversary, and a construction drone called the Dragonfly-6. Alva will also mention that the anniversary sculpture originally appears to have been on the pedestal on the far right, however, meaning that the second door code is 402625.
With the door finally open, players can head through into the remains of Eileen's once luxurious office. Near the desk is another Holo Projector, which, when activated, will reveal that Sasaki wasn't quite as bad as players had first been led to believe and provide the data that Alva and her people have been searching for for so long. After watching the cutscenes, the quest will be marked as complete and players will get some XP and three Skill Points. They'll also unlock the "Recovered Alva's Data" trophy at this time.
Horizon Forbidden West is available now on PS4 and PS5.
