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