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