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