To get the achievement you need to do some steps, it is best you play from the start of the heist, loud & stealth both work.
THIS ACHIEVEMENT CAN BE DONE ON ANY DIFFICULTY

Do these things in this order to unlock the achievement:

• 1. Find & press the button in the first area - Red square on the map below
  
• 2. Find & press the button of the second area - Yellow square on the map below
  
• 3. Find & press the button of the third area - Green square on the map below
  
• 4. Head to the secret location & bag all loot - Blue square on the map below, entrypoint marked with an arrow
  
• 5. Secure all 10 bags of secret loot & escape

In every area there will only be one button you need to press, making it three buttons total.
Use the provided map & images to find these buttons.

GROUND FLOOR:

TOP FLOOR WAREHOUSE:

BUTTON 1
Upper floor, on the balcony railing - outside part:

BUTTON 2
On the stairway beams leading to the upstairs offices:

BUTTON 3
Upper floor, inside the storage room under a storage rack:

BUTTON 4
Outside under cover, near the entrance of the compount, you have jump from those boxes to reach it:

BUTTON 5
Next to the door leading to the office stairway behind some boxes:

BUTTON 1
When you open the security gate, head to the red containers on your left, go inside:

BUTTON 2
Outside, in the foot of a red container:

BUTTON 3
Inside the lonely greenish container:

BUTTON 1
Ground floor, on the stairway beam leading to the harbor office rooms:

BUTTON 2
Ground floor, under the tiny stairway next to the big gate leading to the docks:

Once you have pressed all three buttons, a multi-colored container next to the extraction zone will be interactable:


Open it and proceed to the hidden area, in there you will need to jump on several obstacles to reach a container that is sitting higher than you:

Inside that container will be sitting 10 lootbags, secure them in the Escape Boat, complete the heist and the achievement is yours.