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