Horizon Zero Dawn's The Mountain That Fell continues on from learning about your past in The Heart of the Nora, but it's now time to focus not on yourself, but the world you live in.
This one's located at another towering ruin-mountain hybrid, over at the Bitter Climb. Sylens guides you as usual, but be prepared to explore, as this mission - despite a few enemies at first - is all about discovery.
If you're after help for other parts of the game, consult our complete Horizon Zero Dawn walkthrough and guide.
How to get to the Ruins of GAIA Prime
Despite being creations of GAIA itself, the machines that guard this place will be an absolute nightmare for you to fight in open combat, unless you're significantly prepared and overleveled. For specifics on getting past them, read on to the 'Go to the Ruins of GAIA Prime' section for the details.
Head to the latest waypoint on your map for and climb up the Bitter Climb (heh) using the clearly-marked yellow climbing points as usual.
At the top of the first bit of climbing are a selection of enemies, namely Stalker machines, at first. These can activate a kind of cloaking device that makes them hard work to attack, so focus on deactivating that first by hitting the glowing parts on the side of their bodies, or better yet, sneak past.
After that section is a very tricky area that houses three Watchers, two Ravagers, and three Glinthawks all at once. We highly recommend sneaking past them here, rather than open combat with all of those at once.
Finally, the next level houses a Stormbird which is tricky again - around the same strength as a Thunderjaw in terms of damage and durability. We suggest you tackle it by using a Ropecaster to hold it in place, and some well-placed arrows or slingshot grenades to the glowing, vulnerable areas.
Don't forget to consult your Journal for specifics on which part of its body is weak to what, and keep moving as you fight it to avoid getting nuked by its powerful ranged attacks.
Climb up the Outcrop - Climb up the yellow-gold handholds as usual to the next waypoint.
Talk to Sylens - Sylens isn't here in person, but he helps you on your way nonetheless.
Go to the Door - Head through the door.
Find the Master Override
Now, it's another fairly standard ancient facility. Follow your waypoint and check out any other side passages as you go for hidden trinkets and collectibles. It's a fairly long way, but not a challenging one, so go at your own pace.
Examine the Shrine - You'll seen reach a shrine to Elisabet with a hologram to watch.
View the Hologram - Watch and learn.
Talk to Sylens - Talk and learn...
Search the Ruins for the Master Override - Keep going to your waypoint!
Examine the Control Room - After that lengthy traversal through the mountain, you reach a Control Room that plays home to some ancient corpses. Inside you'll see a holographic playback of what happened.
View the Hologram - Once again, watch and learn.
Talk to Sylens - Another quick chat before it's time to finally get what you came for.
Claim the Master Override - The Master Override is sitting on the far side of the conference table, go grab it!
Return to Sylens' Workshop Follow the waypoint a little longer, before you come outside to a bit of fresh air, and soon a zipline down to a slightly lower level.
Stop before you carry on though! After jumping down off the line, turn back on yourself and scale the rocks to a small purple cave which, at the end, houses another mysterious Power Cell.
Then head back to the bottom of the zipline and climb the rock face directly in front of you there to head back to the workshop again.
Attach the Master Override to the Lance - Back in the Workshop, Sylens is here in person at last, and you can now attach the Master Override to his own Lance, and get yourself a new, stronger melee weapon in the process. Nice!
For more Horizon guides, explainers and advice, take a look at our main Horizon Zero Dawn guide and walkthrough hub, or our advice on finding Horizon Zero Dawn's override Cauldrons for controlling any machine, and unlocking some super-strong armour with our Horizon Zero Dawn Power Cell locations guide, too.
Master Override Lance in hand, you're ready to take on HADES - but the tribes of Meridian aren't just yet. Your next quest, then, means heading back to the city and making final preparations, in The Looming Shadow.