Here is the full list of all 25 Forgotten Chambers achievements.
Use magic 100 times
Use magic 500 times
Find all hidden letters from Chapter 1
Finish the Introduction
Finish Chapter 1
Enchant every book in chapter 1
Exit a room faster than a key
Rewind the clock 10 times
Throw Samuel off the cliff
Pull out all the mushrooms in Introduction stage
Find the key for the chamber of the Great Lotus
Find the key to the chamber of the Crimson Sky
Find the key to the chamber of six pillars
Find the key to the chamber of the magic pot
Solve the starlamp puzzle without hints
Throw a coin into the pond
Complete 3 errands of a goddess
Complete the jigsaw puzzle
Play ring toss game with a puzzle ring
Grab the real stone at once
Find the key to the ivy gate
Use cauldron 10 times
Enchant five wooden rabbits
Feed mushroom to the elephant
Enchant every credits pages