The Forbidden Legacy quest is one of the side quests you can take in the Horizon Forbidden West. You can get this quest from Alva in the Base and the recommended level for this side quest is level 30. This guide will show you how you can unlock the door in the side quest.
Unlock the Door in Forbidden Legacy Quest – Horizon Forbidden West
To unlock the Forbidden Legacy quest, talk to Alva in the base or the Legacy’s Landfall if you are done with the credits. Once you have the quest, you need to search for some data in the ruins first and climb up the Ancestor’s office before you can continue.
After ascending the tower, you will reach a room with a locked door.
You can find the passcode for the first locked door in the next room using the Data points. Nevertheless, you can enter code 102023 to unlock the door.
Keep climbing the tower until you see a Fireglam.
Use the elevator here and you will find another locked door that needs a passcode. This time, the passcode to the door is 402625.
Once you activate the console inside you will get a cutscene and the quest will be complete.
