Subnautica

This is the building at the north end of the mountainuous island North of the Aurora crash site. You'll need a Purple Tablet to get in, but there are a few around in/on/under/inside the island. The achievement will unlock as you walk on deeper inside the building.

The jellyshroom caves are quite near where you start the game, down from the Safe Shallows. There's a base about 300m deep. Inside the base, find and use the PDAs within to unlock the achievement - the PDA you'll need is in the top part of the central area of the base.

To unlock this you must leave a time capsule behind before you leave on the rocket to end the game. The game will ask you if you want to do this - be sure to do so.

An egg can be found in the Deep Grand Reef on the floor inside the Degasi base, pick one up whilst you're down there for Seamonsters. There are only 5 eggs in total though, and it may be possible to lose one - so technically this is missable although it'd be hard to miss it.

To hatch it, you need to build an Alien Containment unit in your base, with a hatch so you can get in and out of it. Once built, place the egg inside and it'll take about 20 minutes to hatch. After it's hatched, pick up the cuddlefish then go outside and drop it to release the fish.

NB you'll need 5 glass, 4 titanium and 1 quartz to build the alien containment and the hatch.

Build a Seamoth - this will likely be the first transportation you craft. The fragments you'll need to scan for this are around wrecks in the Grassy Plateaus area.

Note you will also need a Mobile Vehicle Platform to be able to build and deploy the Seamoth.

This is around 900m deep.

Whilst you're down there, pick up a cuddlefish egg for "Man's Best Friend"

Find the habitat on the floating island, which is in the misty cloud behind the Aurora. There will be a waypoint to it (the "Aurora Rendezvous Point") as you progress through the story.

To unlock the achievement, as with the other Degasi habitat achievements, you need to pick up a specific PDA - in this case its the "Storm!" PDA inside the base in the lowest area.

It'll be very hard to avoid getting this achievement for building a habitat to live in - as this will be pretty much essential to have to survive as you get further through the game.

First you need to craft the Habitat builder, using the Fabricator - for which you'll need a battery, a computer chip and a wiring kit.

You'll likely be doing this in the very early game where materials are scarce and its not yet clear where to find things. The wiring kit requires Silver - which is found in regular resource nodes but only commonly at depths of 60m-90m, so you'll need to dive down a bit to find some.

Then use the tool to construct a piece of habitat, plus a hatch - which will require some Titanium. Any piece of habitat that you can get into is fine, it doesn't have to be a full "Room"; e.g. the basic tubular hallway is good.