Here is the full list of all 23 Hidden: On the trail of the Ancients achievements.
Read all books and notes.
Completed the first part: "On the trail of the Ancients".
Finish the game without using the hints system.
Find and protect the valuable object mentioned by Eneko.
Collect all findings.
Get rid of the creature.
Find and examine all books.
Find the device mentioned by Dr. Laura Garmendia.
Gathers information from the expedition , see what happened.
Complete your mission at the boarding house.
Find and collect information regarding Scopelli's diagram.
Find the artifact which Adriano Scopelli mentions in his letters.
Find and take a picture of the strange idol.
Examine every painting and picture in the boarding house.
Find a way into what used to be Adriano Scopelli's room.
Fix the music box.
«I was in the front during the beginning of the Great War...»