February 15th 2019
The Treasure Hunt note is in front of the barn entrance.
Now go to the back of the barn. There is a tower with a Zipline you can grapple up to. As soon as you grappled up to the top, let go on the Zipline to slide down.
Once off the Zipline, kick in the boards to get inside. Here, you need to crouch to get to the ground level.
At Ground Level, there are two valves you can use. One will open the barn entrance and the other one will move a car so you can get to the other side at the first floor.
Get on the other side and use the 3rd valve. It will move the car that's blocking the way to the stash room. Now you can get in.