Here is the full list of all 15 Mystery of Neuschwanstein achievements.
Solve all lockpicking mini games.
Solve all the hacking mini games.
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.