I did this as a level 24 druid, and I admit I was pushed and died once in the cave. As RickZwet pointed out, the cords of the cave are 38,31, but be aware that to get to the cave you need to go through the main Thistlefur camp, and there are LOTS of 'em - I managed to sneak through in Cat prowl mode right into the cave.

There is a trick in getting to the boxes though - they're concentrated in the first passage to the left as you enter the cave, there is one mob stationed just inside the passage, kill him quickly so as not to agro the wandering shammy.

A few times boxes spawned in the passage itself, but mainly they're in the small area at the end, next to the water.

The mobs spawn in this area at an amazing rate, I would estimate you'd see a complete repop inside five to six minutes, the good point, as mentioned, is that the boxes have the same respawn rate. At any time you'll see two or three boxes spawned in this area, so just hold the position and you'll be OK. Make sure you stick the mobs to the spot or apply a powerful dot at about 10% as they run, so easy to die in such a cramped cave when they run!

Be aware that some of the mobs, especially the little group next to the water, are very hard to single pull, you'll end up pulling two, which is a pain considering they'll still run at 10% and pull reinforcements into the fray.

If you're a rogue, or have stealth talents you can stealth right into the middle of the small passage and take out the wandering shammy before doing any other mobs, it'll help you a lot!

There in Thislefur Hold

The charms are on the ground in little green chests inside the cave

U'll find the charms in little chests.
U gotta move into the cave before u'll see the chests on the ground.
I did this q with my 23 druid not so hard but be carefull with respawns and adds.
GL!

This quest is boring and take some time. you dont get much xp of any items so it's not worth to do it..