Survival Cache 3
Is further up in the "Bells and Carts Room" near the Tidal Caverns. In the story, you have to climb the bells and then cross over with a rope line. On the other side of that rope line, you'll see that - right at the ledge where the line is - there is a climb point down. Climb down, rapple and swing to the downstairs area. Here's the Cache and the Explorer's Backpack.