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It is a Titan, so you have to break runes on its body. Getting to them is the hard part. Climb up at the start and then hang from the ledges, leaping between each one until you can go no further. Then climb up and walk down the little sinew-paved path of ledges until you can't go any further. At this point hang from the furthest ledge and transfer onto the giant ribs.
Traverse those, waiting to jump between them when the ribs are close together. IIRC you will reach a point where you can go no further but a grapple point is visible. Grapple on that and you'll have to repeat the above process, only backwards and on the other side of the Titan. Then you'll reach the first rune.
Once you break that rune the rest is much easier to figure out.