First, you will need to fast travel to Fort Faroth grace.

Go north and jump down a cliff.

After that, go east to another cliff.

Go near the pot next to the cliff.

You have to press O towards tree branch below.

Continue down the following path shown.

Slowly fall down edge to platform below.

Go down a bit before jumping once.

And memorize this spot (useful later).

After that, go down to the bottom following branches.

There is a sleeping giant golem here.

You have to talk to chair Guy.

Get ash of war: Rain of arrows.

And also get Rune Arc next to giant golem.

Battle Giant golem from ground (optional).

Easy way to attack from tree branch.

You can right click to focus on the Giant golem.

Use any long distance attack.

And continue using range attacks.

Giant golem can't reach you from the ground.

Skipping to end (used ranged attacks.

Get Reward: Golem's Halberd.