Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Crack all Vaults.
Complete Meat Circus.
Use the bacon. A lot.
Complete The Asylum.
See yourself through the eyes of many others.
Complete Waterloo World.
Find all Golden Helmets.
Complete Black Velvetopia.
Find Edgar's Secret Garden.
Earn all Merit Badges.
Complete Gloria’s Theater.
Achieve Rank 60.
Complete The Milkman Conspiracy.
Complete Lungfishopolis.
Hear Vernon's Ghost Story.
Achieve Rank 40.
Spy on Bobby's love life.
Complete Milla’s Dance Party.
Uncover Milla's Secret.
Witness Maloof's transformation.
Complete Sasha’s Shooting Gallery.
Achieve Rank 20.
Complete Basic Braining.
Achieve Rank 80.
Achieve Rank 101.
Sort all Emotional Baggage.
Gather all Figments.
Redeem all 16 Scavenger Hunt Items.
Re-brain the Children.
Introduce all Camp Kids to Mr. Pokeylope.
Revisit all brains after completion.
Complete the Punchy Target mini-game.
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.