Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Find all Golden Helmets.
See yourself through the eyes of many others.
Uncover Milla's Secret.
Complete The Asylum.
Re-brain the Children.
Complete Black Velvetopia.
Earn all Merit Badges.
Achieve Rank 80.
Redeem all 16 Scavenger Hunt Items.
Complete Waterloo World.
Complete Gloria’s Theater.
Use the bacon. A lot.
Achieve Rank 60.
Complete The Milkman Conspiracy.
Complete Lungfishopolis.
Achieve Rank 40.
Hear Vernon's Ghost Story.
Complete Milla’s Dance Party.
Complete Sasha’s Shooting Gallery.
Achieve Rank 20.
Complete Basic Braining.
Complete the Punchy Target mini-game.
Complete Meat Circus.
Achieve Rank 101.
Sort all Emotional Baggage.
Crack all Vaults.
Gather all Figments.
Find Edgar's Secret Garden.
Introduce all Camp Kids to Mr. Pokeylope.
Revisit all brains after completion.
Witness Maloof's transformation.
Spy on Bobby's love life.
Give the Coach's speech on the stump.
Read many bulletin board messages.
Discover the secret history of Whispering Rock.
Buy an item from the Camp Store on Christmas.
Cook and consume two different kinds of roast in one sitting.