This was released on June 11, 2013 that is only available for high level Premium members only. The players need to find the three key parts which is when combined will turn to Crystal Skeleton. The key parts cannot be traded to other players so you must find them by yourselves. While hunting for key parts, you can also find rare items and monster drops from level 80+ monsters.

Once you completed the key parts and combined them into Crystal Triskellion Key, you can use the ‘locate’ function for you to locate the treasures as a reward. There is also a chance for you to obtain the new Dragonstone Armor. Even though the key parts are not tradable, the new armor itself can be tradable. This armor can be use by both Free and Premium members.

 

You can find more info here:
http://services.runescape.com/m=news/triskelion-treasures

For Changelog/Patchnote here:
http://services.runescape.com/m=forum/l=0/sl=0/forums.ws?14,15,135,63743300,goto,19