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