Here is the full list of all 60 The Quest achievements.
Reach the good ending of Islands of Ice and Fire
Reach the evil ending of Islands of Ice and Fire
Attain maximum positive fame
Kill The Beast
Enjoy the services of Madame Rosalia's House of Fleshy Delights
Complete Bring Eckinish to Dagma quest
Kill 20 Flesh Eaters
Attain the outfit rank 'Fashionable'
Learn all Attack Magic spells
Perform 2000 melee attacks
Learn all Undead spells
Pickpocket successfully 50 times
Attain maximum negative fame
Perform 2000 ranged attacks
Perform 500 ranged attacks
Find a use for all Idols on Thule and Eldfell
Kill 10 Firebirds
Win 100 card games
Amass 100000 gold
Complete Bribe the sea captain Moruu quest
Find the lost spring
Complete 45 quests
Attain 40 base Endurance
Attain 40 base Personality
Attain 40 base Dexterity
Attain 40 base Strength
Read 12 non-magical books
Travel with the Sea Captain in every port
Cast 1000 spells
Reach the good ending
Reach the evil ending
Find the treasure island
Meet one of the makers of The Quest in game
Complete Join the Thieves' guild quest
Mix 250 potions
Complete 25 quests
Attain 40 base Intelligence
Kill the Cyclops King
Complete Kill the Witch Queen quest
Travel 20000 tiles
Repair 100 items
Kill 250 monsters
Perform 100 ranged attacks
Perform 500 melee attacks
Mix 100 potions
Complete Nobleman's inheritance quest
Cast 250 spells
Find the Abandoned Mine
Mix 25 potions
Kill 100 monsters
Drain 1000 health by using spells
Find the Sunken Monastery
Complete 10 quests
Break out of jail
Get thrown into jail
Perform 100 melee attacks
Complete Matras infection quest
Cast 50 spells
Kill 25 monsters