The Sea of Sands is a main quest in finding POSEIDON in Horizon Forbidden West.
Your objective is to head to the old Las Vegas to find and retrieve POSEIDON.
Here’s a walkthrough of The Sea of Sands in Horizon Forbidden West.
Recommended level is 22 and above.
Investigate the Flooded Ruin
To begin the quest, head to the Flooded Ruin. This area was once known as Las Vegas in the old world.
The exact location is shown in the map below, marked by the quest symbol.
When you arrive, you’ll see a building with water flowing out of it.
Climb up the ladder and enter the building. You’ll hear voices from outside.
Inside, you’ll meet Morlund and his crew. Talk to him.
Go to the Machine Herd
There are two things you need to get. The first one is from the Machine Herd just south as shown in the map below.
As you reach the location, use focus and follow the tracks.
You will then reach a Machine Herd. Take out the two smaller machines first.
After they’re dead, continue to follow the tracks until you reach the rest of the herd. Take them out and loot them to find the machine knee cap.
Recover the compressed air capsule
When you’re done, head back to Morlund.
Now, dive underwater to look for the air capsule.
Keep going down and you’ll see the air capsule. Retrieve it and surface.
Give the parts to Morlund to make a diving mask.
Use the workbench to make the diving mask.
With the diving mask, you can breathe infinitely underwater.
Just dive back in and go all the way down.
Continue to make your way underwater.
You will then see a huge machine from far. Swim towards it.
As you try to approach, the current will sweep you away.
Investigate the red light
The objective will be updated. Head to the red light at the opposite.
You’ll see a console inside.
Find the primary pump node
Now you need to find the primary pump node.
Look for a hole that leads further down.
Enter the tunnel and continue to swim to the next area.
To resurface, look for the ladder underwater.
You will then see a valve. Activate the primary pump node using the valve.
Once you’re done, return to the Sunken City.
Find the secondary pump node
You’ll then need to find the second pump node. Watch out for the machines underwater. You can hide inside the coral reef while the machines swim by.
Then, look for the tunnel entrance under an archway.
Like before, find the ladder to resurface.
Then, ignite the Firegleam.
Open the valve after the Firegleam is gone.
Find the pump maintenance station
Next, look for the maintenance station as shown in the map below.
You’ll see a building with a few floors.
The entrance is towards the bottom of the building, on the left.
Swim low and you’ll see it.
Enter the building via the crack and make your way up.
At the top, activate the emergency purge to get rid of the water.
Continue to find POSEIDON
Make your way out of the building.
Once you’re out, you can face the machines on land. Take them out if you must.
Kill the Tideripper
You’ll then have to face the biggest machine here called the Tideripper. Use focus to find the weak spots.
I personally used a boltblaster and hid behind the rock. It made the fight much easier.
Talk to Morlund and crew
After the battle, wait for Morlund and the crew to come down from the platform, or the dialogue won’t load.
Talk to him (optional).
Now, head to the door which was guarded by Tideripper.
Enter the room and you’ll find POSEIDON.
Insert GAIA Kernel to retrieve POSEIDON.
Return to the elevator shaft
Now, head back up to the elevator. Use the grapple points to go up.
Deliver POSEIDON to GAIA
After the cutscene with Morlund and the rest, head back to the base to deliver POSEIDON to GAIA.
The quest ends here.