Navigate the treacherous Styx and descend into Hell in Subnautica. This guide covers the Blood Kelp Zone, Lost River, Inactive Lava Zone, and alien bases.
So to start our journey, we need to make our way to one of the openings that will take us down. There is a good chance you may have stumbled upon some entrances here and there. The entrance I always find easiest to locate and initially navigate is the entrance in the northwestern Blood Kelp Zone. If you had to go to the databox by Lifepod 2 to unlock your first Cyclops depth module, then you will most certainly have seen the entrance. It is a giant cave mouth that cannot be missed. It also has an adult Ghost Leviathan patrolling around, so take caution. If you take the western Blood Kelp Zone trench instead of this location, it lacks large predators, but the trench is a lot more narrow and more difficult to navigate initially. Both entrances will eventually lead to the same place.
Start your descent and navigate the caves involved. If the lighting becomes bright and green, you're in the right place. This biome is called the Lost River. Be careful of the green brine pools that litter the floor, they are corrosive. There are some skeletons here you can scan for more insight into things. This location is the first time you will encounter nickel, so make sure you gather some and immediately upgrade the depth module for your Cyclops and create your Prawn Suit's first depth module (which will require making a moonpool). They are mostly okay in this biome (some parts of it can go down to 1000m, and your cyclops can only handle 900 right now), but we're trying to go deeper.
Once your depth modules are upgraded, navigate the Lost River, looking for a way down. If you come across an area where the brine pools are replaced with harmless glowing blue pools and a big, unique tree, you're in the right place. Go past that tree and you should find what you're looking for.
Going down deep enough will lead you to lava. This is the Inactive Lava Zone. Despite what the name may first make you think, the lava here is very much hot and still molten and lethal to your squishy human body. Do NOT go near it outside of your Prawn Suit, you will die instantly if you touch it and even being near it will burn you, even with the reinforced suit.
You're in the right place once you hit a big, circular cavern with what looks like a small mountain in the middle. There is a way inside that mountain and you should try to find it before you bother trying to go down further. Your cyclops won't fit inside the mountain, but your Prawn Suit sure will. Remember the tablets we made earlier (or brought the mats for)? Now is the time to craft them and stuff them in your inventory before you go in this part.
Predator Warning! Inside this cave lurks a couple of leviathans known as Sea Dragon Leviathans. They are extremely lethal and highly aggressive. They can also shoot fireballs. Yes, underwater. And it's rapid fire. And hurts like hell. Your Cyclops will not save you, they will attack your Cyclops.
To avoid the predators in the area, make sure you move at the slowest speed you can and run the silent mode when you can spare the power. It's better than cavitating and causing your Cyclops to draw the attention of the local wildlife.
Once you find your way inside what is inside the mountain (you'll know it when you see it), make sure to pick up any more Ion Cubes you find. There is also an Ion Cube mining node inside, so make sure you bring your Prawn Suit in that far if you have the drill arm.
There are two doors that need a purple tablet and you should not leave without getting what is behind both of them. One has a blue tablet, the other has the blueprints for the Ion Battery and the Ion Power Cell, both of which have five times the capacity of their non-ion counterparts. They will take longer to recharge, but it will be a long while before you need to charge them at all. At the very least, you should try to craft a Ion Power Cell when you get back to the Cyclops and swap out the normal power cell in your Prawn Suit for the new upgrade. If you have the materials, feel free to pop a few into the Cyclops as well. Just save an Ion Cube to make a Blue Tablet. You will need 2 for the final facility in the game and the one you picked up is the only freebee the game gives you.
Once you've gotten what you need, leave and return to your cyclops. Try to find a way to go even deeper. If you're having trouble finding a way down, there is a pit north of the "mountain" in the middle of the cavern. It is mostly just a circular pit with nothing in it, but one of the walls of the pit has a tunnel that dumps out into another lava area.
If you find a large cavern with another leviathan and an alien base, you've entered the right place. Get your cyclops close to the base, grab your Blue Tablets (you need 2), and ride your Prawn Suit into the base. You'll need it.
In the middle of the base is one of the most amazing creations: a respawning Ion Cube node. Which is good, because you're about to need them.
For the sake of you not running around throwing yourself in loading screens for nothing, I'm going to give as brief and lightly-spoilered a description as I can of the interior.
You'll notice a lot of doors coming from the main room of the base. The doors to your left and right have things to scan and lore to learn. The door directly ahead, blocked by a forcefield, is the moonpool of the base and requires a blue tablet to open. The doors on the diagonals of the room all lead to Alien Arches. If you haven't messed with these before, you simply put an Ion Cube in the pedestal and it becomes a two-way warp between itself and another arch assigned to it. These will become important soon, but for now, you should ignore the arches, other than maybe activating them if you want. They go to various biomes in the world, but nothing ground shattering or particularly secret.
Go through the forcefield door. Jump into the moonpool. I suggest staying put so you don't miss the event that happens. Feel free to sink lower in the water to get a bette
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