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