Velvet Assassin
45 Achievements
1,000
15-20h
Curiosity
You have found all letters during a campaign
30
How to unlock the Curiosity achievement in Velvet Assassin - Definitive Guide
Here's a walkthrough with the collectibles bolded. It isn't as good as the old one, but it's still decent.
http://wikicheats.gametrailers.com/Velvet_Assassin_-_PC_XB36...
Letters are scattered all over, you must collect them on a single playthough, you can't reload a previous mission as this isn't a stackable achievement it must be done in a single playthough.
Maps with all the locations are under the "Eagle Eye" achievement listed above. Each letter is marked with a quill on the map.
Letter 1:
Location: The Lost, Fuel Storage - Can be found on a desk.
Letter 2:
Location: Death Of The Butcher, Crypt - On a small desk on your exit to the level on your right side.
Letter 3:
Location: Leave A Light On, Docks - In the middle of a room with an office desk.
Letter 4:
Location: The Third Man, Sewers - On top of a crate located next to a ladder.
Letter 5:
Location: The Third Man, Ghetto - In a small room which is opened with a key, the letter is on a small table in the corner.
Letter 6:
Location: The Third Man, Prison - On a bed in a cell located on the first floor.
Letter 7:
Location: Le Boeuf - Found in the basement of the Boathouse.
Letter 8:
Location: Fade To Grey, Hospital - Found on a desk which has a corpse in the chair and a wardrobe behind the desk.
These are just rough descriptions, use the maps provided under "Eagle Eye" to find each location.