WoW - Key to the Palace of Lei Shen

As I was tooling around the Isle of Thunder I picked this up. Not sure whether it was from a rare mob or a chest. I wondered what it die.

Well, it turns out that it opens up a quest called Treasures of the Thunder King which you can get from Taoshi who is underneath the waterfall at 51,46

You can only loot this key once per week but you can stack them up and use all you have one after the other.

It lets you in to do a loot run and there are achievements available too. Look it up on wowhead.