Here is the full list of all 45 The Forest achievements. It takes around 50-60 hours to unlock all of the achievements on Windows.
Pass 50,000 steps
Play through entire game without killing or eating animals. Alone in Single Player or together in Multiplayer.
Find all missing passengers
Eat all mushroom types
Finish Game
Collect all robot pieces
Explore all caves
Revive 10 co-op players
Collect all cassette tapes!
Revive one co-op player
Kill all animal types and display heads
Cut down 1000 trees
Set off 20 bombs
Share a weapon in MP
Craft 10 medicine items
Catch fish with a trap. Alone in Single Player or together in Multiplayer.
In Single Player, don't kill any cannibals for more than 10 days in a row
Craft all items
Kill shark. Alone in Single Player or together in Multiplayer.
Grow all plant types
Eat an entire family
Knock down 6 or more trees with 1 explosive. Alone in Single Player or together in Multiplayer.
Sleep on yacht
Kill 6 or more fish with a stick of dynamite. Alone in Single Player or together in Multiplayer.
Chop up 50 bodies
In Single Player, kill 100 cannibals
Repair a shelter
Use the compass
Kill bird with arrow
Cut down 100 trees
Build a super long wall
Share a food or drink item in MP
Killed downed enemy with rock
Survive 5 nights
Eat an enemy
Make and wear stealth armour
Kill a bunny. Alone in Single Player or together in Multiplayer.
Survive 1 night
Sleep with another player (group sleep)