How do you find the third charm?

Answer from: cool123
You have to defeat the monsters then when the bridge goes down you see the white charm

Answer from: Thunder
While the previous answer is not technically wrong, it lacks specific details.

The third charm, the wind charm, is located in the Coastal Cliffs level (2nd level), I'd guess about 1/3 of the way through. You will pass a chest and a blocked path that require you to need this charm - don't worry, the game's path has you backtrack once you get the charm, so passing those is not an issue, you will come back to them.

Once you are inside the castle area you will fight a golem and some boar-like creatures, all with vulnerability to the wind charm - but you won't get it until after you defeat them. The boar-like creatures are a PITA because they charge you. There were 3 of them, one at a time, with the golem attacking the entire time - kite* them around, doing damage with your bow. Use your dodge skill and just take your time. This is what worked for me, if there's a faster way to defeat them without already having the wind charm, I don't know it.

Once you defeat these guys, a path will open with the charm beyond. Go get it, then use it to continue your path. You will come out of the castle through the large opening that you saw earlier in the level - the large "window" that Merida couldn't jump to.

*If you don't play WoW or other games where knowing how to kite on a ranged class is useful, what I mean by this is just keep moving, leading them around, and stay out of their area of damage.

Answer from: angus
The second answer is right, or at least that is what happened to me.