Here is the full list of all 25 The Keep achievements.
Finish Chapter 3: Dungeon.
Save at least one child.
Find Nataniel.
Finish Chapter 2: Prison.
Find at least one hideout.
Cast at least one spell.
Finish tutorial.
Finish Chapter 1: Tower Entrance.
Kill at least one enemy.
Use at least one melee combo.
Save all children.
Finish Chapter 4: Lower Dungeon.
Finish Chapter 5: Dwarves’ Lair.
Finish Chapter 6: Upper Mine.
Finish Chapter 7: Mining Site.
Finish Chapter 8: Abandoned Mine.
Finish Chapter 9: Watrys’ Labyrinth.
Finish Chapter 10: Watrys’ Tower.
Finish game on hard difficulty.
Finish game on permadeath.
Kill all enemies.
Find all hideouts.
Use all melee combos at least once.
Cast all spells.
Discover the hidden ALTernate ending.