Here is the full list of all 30 Valley achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Collect 100 acorns
Drop down the pit located in Proving Grounds
Collect enough medallions to access all pyramid chambers
Kill 50 trees
Take life from 20 animals
Defeat the Alpha
Acquire all upgrades for the L.E.A.F. suit
Complete Camp Henday
Complete the Proving Grounds
Complete Smoke Lake
Complete the Astra Facility
Take 10,000 steps
Gain entry to the Sussurian Pyramid
Gain entry through all the acorn doors
Defeat 25 dark creatures
Find Virginia's music box
Stop the Astra Facility from killing the valley
Collect all energy upgrades
Discover the secret Landshark encampment
Spend 20 minutes of accumulated time in mid-air
Find all 8 pages
Complete game without the valley dying
Complete the Soma Reactor
Acquire the Lifeseed
Complete the Soma Facility
Pacify 10 amrita swarms
Complete Titan Rock
Revive 100 trees
Complete Susurrus Valley
Complete Wendigo Lake