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