Forbidden Legacy - Horizon Forbidden West Guide - IGN (2024)

Forbidden Legacy is a CompanionSide Questyou receive from Alva at the Base.This Horizon Forbidden West Forbidden Legacy walkthrough will contain information on how to find code to unlock the door, who to talk to, what to do, and any tips or tricksto help you defeat machines that come your way.

In this Side Quest, Aloy helps Alva look for data on a flood control system called Leviathan that could help the Quen.

Forbidden Legacy Guide

Now that Alva has settled into the Base, she has been sorting through all the data she acquired from the Greenhouse. In the data she found information about Leviathan, a network of river gates and underground tunnels used for flood control. The Quen tried to duplicate the system but never got it to work. The data from the Greenhouse mentioned a facility in San Francisco where Leviathan was created. Alva believes if she can get that data, then the Quen can fix their system. Aloy agrees to help her.

Go to Legacy's Landfall

Head to Legacy's Landfall and call Alva from the Campfire. Together they look for the Diviner who might know where the facility is, Nirik. He tells them about the ruins and to avoid them, but he's hiding something. Alva convinces him to talk.

Follow Alva to the Research Facility

Follow Alva south towards the research facility. Once they get there they will have to find a way in. Before they can explore any further, they hear a rumbling and a Slitherfang appears. Defeat it.

Kill the Slitherfang

The Slitherfang is a Heavyweight Combat Machine. It is weak against Fire, Frost, and Plasma damage and strong versus Shock, Purgewater, and Acid damage. It has the following components, abilities, and weapons:

• Sonic Hood: These metal plates all along its head control the Sonic Blast attack. They are vulnerable when extended, but detach them and you will disable the attack.
• Earthgrinder: Located on its chest, this is a key upgrade resource. Detach it with Tear damage.
• Glowblast Canister: Found right below its head, these will explode when shot with Plasma damage.
• Metalbite Sac: These are located just below the Glowblast Canisters. When this sac is destroyed, it explodes and you will disable its Acid attacks.
• Sparker: Found below the Metalbite Sac, these will explode when shot with Shock damage.
• Purgewater Canister: These canisters can be found on the body of the Slitherfang. When shot with Purgewater damage it will trigger an elemental explosion.
• Resource Container: Found along the back of the machine, this contains valuable resources so detach it if you can.
• Data Nexus: This central processor is located on the back of the Slitherfang's head. It is a weak spot so it is vulnerable to damage.
• Purgewater Sac: This is found below the Data Nexus. It will explode when destroyed. This also controls the Purgewater attacks, so once it is destroyed, the attack is disabled.
• Shock Orb: These orbs can be found near the tail end of the Slitherfang. These power its Shock attacks, so detach it if you can. Once you do detach it, it can be used as a heavy weapon.

The Slitherfang is a tough machine to fight, but it has plenty of weak spots. It is a very large machine so it will have slow maneuverability. It will usually coil itself on a nearby tower. Use this opportunity to hit its weak spots including the canisters and sacs. Spike Throwers will do a lot of damage to it, so have those available. Watch for the head slams, tail whips, and Sonic Blast attacks. It also has an attack where it will dive into the ground and pop up intermittently. Try to dodge out of its path, if you can.

Search the Ruins for the Data

Once the Slitherfang is defeated search the ruins. There is a rectangular building on the right of the Slitherfang fight that has a vent you can open. Go through it into the water. Go forward and take the submerged stairs to the left to get out of the water. Move forward under the stone beam and take the ramp on the left to get to the second floor. Jump across, grab onto the ledge and lift yourself up.

Go along the pipe to the right and then another pipe, and jump. Follow the path and there will be a console to the right. Activate the Holo Projector and listen to the audio recording from Eileen Sasaki. You'll learn that the Leviathan data was sent to a nearby building.

Follow Alva to the Atbay Headquarters

Follow Alva. When they reach the Headquarters the entrance will be blocked. Follow Alva knows of a passageway in the nearby ruin. Follow her. At the Campfire, climb up and go left along the path.

Find an Entrance into the Atbay Headquarters

There will be a blue metal X on a wall. Use the Pullcaster to create a hole. Go through and climb up the elevator shaft. Use the Focus to highlight the yellow handholds. At the top of the shaft, Aloy will pull herself up to a platform. Use the Pullcaster to bring down the sturdy beam in front of you. Cross over and there will be a ladder on the left. Shoot the red holder to release the ladder and climb up.

There will be two Glinthawks perched on the floor above. You can fight them or go right and sneak past them. If you choose to fight them, you can sneak behind them and Silent Strike. Chances are you will clear them in one shot.

Jump to the Tower

Climb the wall on the left to get to a landing, then climb the wall on the right. Go forward onto the beam and pull the debris across the gap. There will be two blue metal clamps to use the Pullcaster on. Jump over and wait for Alva to jump.

Search the Headquarters for the Data on Leviathan

Keep going and you'll find a security door and console. You'll need a passcode to open. Look around and scan the two Datapoints for information. The code is . Enter and go through the office. There will be another audio log to listen to from Eileen Sasaki and her father, Kenzo. Go through the door on the left. There will be a Campfire on the right. There is rubble that needs to be cleared in the elevator shaft to the left. Use the Pullcaster to grab onto the metal clamp.

Climb up to the Ancestor's Office

Go through the hole and go right to climb up. Use the grapple point to get you onto a beam. The beam will fall and there will be additional beams to jump along. Pick up the Greenshine and then keep climbing up and around the building. Follow the yellow handholds. Get to the ledge, walk onto the beam, and use your Pullcaster to open the vent door to reveal a grapple point. Use it to clear the gap. Drop down to the handhold below and then jump to the handholds on the wall opposite you. (Be careful here the drop down can be tricky). Climb up the wall and jump to the beam behind you. Turn around and look up at the wall behind you. There will be a beam with a blue metal clamp above you that you can bring down with the Pullcaster (it might be hard to miss as it won't light up when the Focus is used). Jump onto the beam and then jump to the ledge on your left.

You will use the Pullcaster three times to get to the top. Pullcaster, turn right, Pullcaster, look up, and Pullcaster to the top. Go through the door on the left. There will be Firegleam to ignite that will open up the way to the elevator shaft for Alva. Go up the shaft and jump into the opening. This will lead you to Eileen's office.

How to Unlock the Forbidden Legacy Door

There is a locked door and you will need the passcode. Activate the Focus and scan the room. There will be four artifacts in the office of special significance. As you scan each Artifact, Alva will give Aloy information about each of them. Every number she says will be part of the code you need: 40, 25, 2, and 6.

The code is (because the artifacts are out of order).

Go inside and activate the Holo Projector and listen to the holo message from Eileen. Alva will then receive the Leviathan data. You can glide down from the tower after the Quest ends.