Here is the full list of all 26 Unravel achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Collect all achievements
Finish each level from start to finish without dying
Find every secret
Break all the ice on the way to the letterbox in one go
Find the secret in the crushing, zapping death machine
Use the excavator to find a secret
Make it to the water wheel without using a log raft
Make it through the mire in one go without swatting any mosquitoes
Find the secret hidden in the tree tops where you fly
Tear down all the thistles in one go
Mend a broken bond
Use your lasso to jump between 25 different points without touching the ground
Find the other broken half piece
Find a broken half piece
Find the secret in the engine room
Find the eighth missing piece
Clear all the snowy branches in one go
Find the seventh missing piece
Steal the sixth missing piece back
Find the sixth missing piece
Find the fifth missing piece
Find the fourth missing piece
Get the secret hidden in the mountain maze
Find the third missing piece
Find the second missing piece
Find the first missing piece