Welcome to the Subnautica 100% achievements guide. This guide explains how to unlock all 17 achievements.
This guide was made by me from my own experience of Subnautica. Please ask if you would like me to make a change, or if you would like to use the guide in any way.

This section includes the achievements that are not related to the story, and will not spoil it for you.

Getting your feet wet
This one is hard to miss and is unlocked by simply jumping in the water.

Personal Propulsion
You must scan 3 Seamoth fragments with your scanner, and construct the Seamoth on your Mobile Vehicle Bay
Requirements:
Scanner, Seamoth blueprint, Mobile Vehicle Bay.

40-foot sub for one
You must scan 3 Cyclops engine fragments, 3 Cyclops bridge fragments, and 3 Cyclops hull fragments, and construct the Cyclops on your Mobile Vehicle Bay.
Requirements:
Scanner, Cyclops blueprint, Mobile Vehicle Bay.

Ordered the Prawn
You must scan 20 Prawn Suit Fragments (3 in the Aurora), and construct the Prawn Suit on your Mobile Vehicle Bay.
Requirements:
Scanner, Prawn Suit blueprint, Mobile Vehicle Bay.

"Man's best friend"
You must find a Cuddlefish egg and incubate it in Alien Containment until it hatches, then release the Cuddlefish in a preferably safe location.
Requirements:
Seabase, Cuddlefish egg, Alien Containment.

Settling in for the long haul
You must craft the Habitat Builder in your lifepod's fabricator, and construct a corridor, or room.
Requirements: Habitat Builder.

This achievements are related to the story and contain unmarked spoilers.

Extinction Event Avoided
You must repair the Aurora's drive core using the Repair Tool.
Requirements:
Seamoth, Seamoth Perimeter Defense System (for if a Reaper Leviathan attacks), Repair Tool.

Seaside Living with an Ocean View
You must travel to the Floating Island and visit the main Degasi Base that's not on the mountain.
Requirements:
Any vehicle, Survival Knife (recommended), Scanner (recommended).

Follow the Degasi
You must travel to the Jellyshroom Caves and visit the Degasi base inside.
Requirements:
Seamoth (recommended), Seamoth Depth Module MK1 (recommended), Repair Tool (If using Seamoth).

Seamonsters
You must visit the final Degasi Base in the Deep Grand Reef. This one is much more daungerous then the others, so be careful. This base also contains a Cuddlefish egg which can help with unlocking "Man's best friend".
Requirements:
Cyclops, Cyclops Depth Module MK1 (recommended), Prawn Suit, food & water, Scanner (required for scanning things), Stasis Rifle (recommended), Repair Tool.

Ancient Technologies
You must visit the Mountain Island and visit the Enforcement Platform.
Requirements:
Any vehicle, Purple Tablet 2X (found on island), Survival Knife (recommended), Scanner (recommended).

Follow the Lost River
You must visit the Disease Research Facility found in a cave in the Lost River Mountains Corridor.
Requirements:
Any vehicle (preferably Seamoth), food & water, Scanner, Repair Tool, (required for scanning things), Purple Tablet 2X.

Thermal Activity
You must visit the Alien Thermal Plant in the Inactive Lava Zone's Lava Castle.
Requirements:
Cyclops, Cyclops Depth Module MK2 Prawn Suit, Prawn Suit Depth Module MK1, Purple Tablet 2X food & water, Survival Knife, Scanner, Stasis Rifle (recommended), lots of Medical Kits, Repair Tool, Reinforced Diving Suit (recommended, cannot leave vehicles without).

Fourteen Thousand Leagues Under the Sea
You must visit the Primary Containment Facility in the Lava Lakes.
Requirements:
Cyclops, Cyclops Depth Module MK3, Prawn Suit, Prawn Suit Depth Module MK2, Blue Tablet 2X, food & water, Survival Knife, Scanner, Stasis Rifle (recommended), Reinforced Diving Suit (recommended, cannot leave vehicles without), lots of Medical Kits, Repair Tool.

Optimal Health
You must cure the infection after hatching the Sea Emperor Babies by touching the Enzyme 42 they spit out.
Requirements:
Sea Emperor Babies Hatched.

Leave Only Time Capsules
You must launch the Neptune Escape Rocket and deploy a Time Capsule for another player to find.
Requirements:
Neptune Escape Rocket launched with Time Capsule.

Go Among the Stars
You must launch the Neptune Escape Rocket and complete the game.
Requirements:
Neptune Escape Rocket Launched.

Thank you for reading my guide and congratulations. Enjoy your achievements.