Here is the full list of all 20 Ghost of a Tale achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Finish every secondary quest.
Complete the game without getting hit by an enemy.
Complete the game without alerting any guards.
Set fire to all inflammable items in Dwindling Heights.
Reach the end of the game.
Complete the game without ever eating to regain energy.
Complete all of Gusto and Fatale's quests.
Learn all skills in the adventure.
Unlock forty-five footnotes.
Complete the full set of Duinlan's armour.
Rid Dwindling Heights of all spiders.
Play all songs during the course of the game.
Discover the name of every possible character in Dwindling Heights.
Steal all of the Rat Guards' handkerchiefs.
Reach the desolate shore.
Discover Duinlan’s tomb.
Open all window shutters.
Gather fifty-five mushrooms.
Reach the highest point in the highest tower.
Escape from Tilo’s cell.