This is a cache of one of the four Nobel houses of Westeros. In order to find and sit upon The Iron Throne you will have to visit each of the four houses to gather information that will reveal its location. Once you have claimed the throne you will rule over the entire realm, at least until the next Machiavellian schemer tries to remove you from your seat by fair means or foul, or most likely the removal of your head.
You are looking for a small camo'd clip lock which contains information to help locate A Cache of Ice and Fire - The Iron Throne.