In Barrels Out of Bound in the Deep Water Caverns (Rescuing Thorin), where you first come in there is a platform with vines. Climb them and jump on the ropes to the left and around the bend until you see the blue crystal. Later you will be able to get Master Throwing Tactics, which is in a cave to the left of the main gate (after you put the dwarves in barrels without opening the gate). Then up on the ledges, go right and follow the path attached to the wall. You will see a barred gate and a switch. Insert Opening Crystal #4. In that cave you will find Master Throwing Tactics and some jewels.