The Tower is the fourth level of Sifu.To unlock the achievement you have to find the 15 collectibles. Some of them are automatically unlocked as you progress through the level. I will list them anyway.
Below is the board collectibles with numbers:
Collectible #1 -
The Sanctuary - When you reach the control room you will have to fight some enemies. After this, you reach a small room with a big screen on the left, and four enemies. The collectible is at the bottom of the screen. This is a flyer for the Sanctuary.
Collectible #2 -
Employees - At the start of the mission, when the receptionist welcomes you
Collectible #3 -
Jingfeng's Computer - When you first play the level, go to the left elevator. You will step out inside Jingfeng's office and she will have a quick words for you. Then kill her 3 guards and go back to her desk. You find the computer here.
You also unlock a new choice for the conversation with the Tech Guy (mission 2) to get the Hacker's Key
Collectible #4-
Elevator - This is the elevator on the right at the start of the level. Call the elevator to unlock this collectible
Collectible #5-
Shadows - Automatically unlocked when dark assassin's attak you during the elevator fight
Collectible #6-
The Guardian's Vow - Obtained inside Jingfeng's safe (#12)
Collectible #7-
The Rift - As you go deeper into the Tower, your surroundings will transform thanks to Jingfeng's bell toll, adding this entry to your board
Collectible #8-
A Conspiracy - Automatically unlocked when reaching the room where Hui Su is waiting for you (#9)
Collectible #9-
Hui Su - As you descend through the Rift, you will come across a lone female warrior looking at a large wall of scrawled papers. Defeat her to add this entry to your board
Collectible #10-
Sun Mei - Similar to #9, Sun Mei will be waiting for you in a room with various weapons. After you take her down, you will get this entry added to your board
Collectible #11-
Elevator Keycard - Obtained upon defeating Sun Mei (#10)
Collectible #12-
Jingfeng's Safe - Once you get the Hacker's Key (from mission 2: The Club), go back to Jingfeng's office (left elevator) and interact with the computer. You will see the safe opening on the right. Inside is the Artist's Key (#14) as well as the Guardian's Vow (#6)
Collectible #13-
Art Auction - At the beginning of the mission where the receptionist is: go to the left inside the room with the sofas. The collectible is lying on a table
Collectible #14-
Artist's Key - Inside Jingfeng's Safe (#12)
Collectible #15-
The Dawn - After progressing through the conference rooms, you will come across a small square room with enemies debriefing. After defeating them, the Dawn logo will appear on a TV screen and will be added to your board. Also automatically unlocked inside the room where Sun Mei waits