This guide will let you find the Lava Lakes/Active Lava Zone in Subnautica.
Starting from the coral tube sticking up out of the water, you will need to make your way about one bump to the right of northeast until you reach a large drop with a large cave entrance in the bulb zone.
It is recommended to have a cyclops with an Mk3 depth module and sonar or a prawn suit with an Mk2 Depth module. You will also need a grapple arm, an ultra or high capacity O2 tank, a sea glide, and a reinforced dive suit.
The main threat you will encounter is the sea dragon leviathan; you have to avoid them, the lava lizard, which you can either avoid or kill using the knife and stasis rifle.
You will also face the warper, which can warp you out of your vehicle unless you are in the cyclops. But if it warps you, you can either run from it or do enough damage to it until it warps away.
There is also lava larva in the lava zone that latch on to your cyclops and drain energy from it, so you can either get the thermal reactor for the cyclops or bring extra power cells and take out power cells when you aren’t in your cyclops.
The coordinates for this location are (81.7, -1321.4, 352.3).
It is the drop and entrance you are looking for.
Once you reach the entrance, you will need to continue through it and eventually reach the lost river. You have to look for a large hole that will lead to the inactive lava zone.
There is also a good chance of a ghost leviathan swimming around/above the large hole you are looking for. You have to avoid it and get down the hole as quickly as possible.
Here is the large hole you’re looking for.
Once you’ve reached a large area that looks like this, you will see the lava castle straight ahead. You have to head left of the lava castle and look on the seafloor for a large opening/hole that, once you go down it will lead you to the lava lakes/Active lava zone.
