"Grab the climbing backpack and look straight up. You’ll see a shiny grappling hook. Click it.
Face north. Now head WEST towards the first stalactite you can grab. Keep clicking stalactites until you’ve gone around to the other side and started grabbing onto wall rocks. Make your way around, and start looking for the bag with the key. Get close enough and click it.
Now drop down to floor, use the same grappling hook again, but this time, head EAST, clicking stalactites until you get to the climbing rocks. Click the climbing rock on the opposite side of the wall you’re on for the last step, the look back towards the other side where you’ll see a chest and a new grappling hook. Click that new hook, but DO NOT drop off. Click the chest while you’re on the grappling hook to complete the quest.
HINT 1: Do NOT use 1st person camera, for some reason some of the stalactites clicks do not register in 1st person camera mode.
HINT 2: Watch out for the bat patrolling around as you click around."
That is what Wowhead says. But, I get there and the new grappling hook won’t let me engage.
I’m quoting Wowhead because support always sends you there first when there is a problem.