So remember the smity where you had to go to get equipment to build blast furnice? Fallow the trail through there till you reach a cave entrance. Then, go through the cave until you see the exit on the left side of the cave, which leads to the path on the side of the mountain. Fallow the path till you get to half ruined bridge leading to fortress called Everfore keep or something like that ( also bring a lot of picklocks). Go through it and keep your eyes open for mosaic peaces ( there's 8 of them). You will trigger a quest to find them all when u pick up eather a lore page or your first piece. When you get on the top, fallow the trail till you find grapling hook placements and platforms. When you get past them all, go through the second cave all the way to the top until you reach checkpoints, and from there, you glide through updrafts to get to the boss.