Here is the full list of all 15 Mystery of Neuschwanstein achievements.
Complete chapter VI.
Find all of Ludwig's diary pages.
Discover a tomb.
Complete chapter V.
Complete chapter IV.
Repair the shredder and the dynamo.
Listen to Ludwig's Parrot.
Complete chapter III.
Analyze rock samples and Ludwig's letter.
Take a finger print.
Complete chapter II.
Complete chapter I.
Find any of Ludwig's diary pages.
Solve all the hacking mini games.
Solve all lockpicking mini games.