Here is the full list of all 40 Legend of Grimrock achievements. It takes around 35-40 hours to unlock all of the achievements on Windows.
Throw a rock 100 times
Mix 50 potions
Find 5 skulls
Find all secrets
Find the pie
Perform 250 unarmed attacks
Finish first level in under 4 minutes
Complete the game
Find all treasures
Collect and wear full set of plate mail (5 pieces)
Collect and wear full set of Valor armor (6pieces)
Get into the Prison
Give Toorum a hand
Open all iron doors
Find Zhandul's Orb
Collect and wear lurker's wardrobe (4 pieces)
Perform 500 ranged weapon attacks
Solve the Checkered room puzzle
Find Dismantler
Kill a monster by dropping or teleporting on it
Find entrance to the Vault of Dismantler
Find 50 secrets
Collect and wear full set of chitin armor (4 pieces)
Survive the invasion of white blobs
Jump 25 times into a pit
Kill 250 monsters
Cast 500 spells
Kill your first ogre
Mix 10 potions
Travel 10000 tiles
Find 25 secrets
Survive the slimes
Cast 250 Spells
Find 10 secrets
Perform 500 melee weapon attacks
Cast 25 spells
Complete the game with hard difficulty setting
Complete the game with old school mode
Backstab a monster
Obtain level 50 in any skill