Grab the ladder from the staircase to the grindstone (right side of the furnace, in the main room)

Go outside by the tanning racks, then place the ladder next to the door leading to the reception desk. You have to stand near the wall, then look straight at the wall (somewhere around the default eye level) and try to place it. It might take you a few tries, but the end result should look something like this:

Climbing the ladder is pretty simple, just jump onto it and hold W. Now for the actual jump, you might need to practice it a bit (alhthough it is pretty simple).
You need to look slightly left of the window, then holding only W and Sprint, jump off towards the window. Now the key aspect is that you have to turn towards it using only your mouse. Don't need to press A or D, mouse should be enough. Try it a few times and once you get it right, you'll be able to do it with no problems.

Congratulations, you've arrived upstairs and you can create some leather grips! Now for the actual acquisition of the leader, you should practice dropping down safely to the outside level.
From the window, you should aim right towards the stones by the wall. Alternatively, you can try and hit one of the brown beams on the walls (they're actually sticking out, so can be used as surfaces)


The rocks are slightly right from the center of this screenshot. Try aiming there, and you should land safely. If you keep fainting, try doing it without jumping.

It's a very simple trick but once you nail it, the challenge level should be pretty easily roamable for you