Imagine you're Thorin Oakenshield, son of Thrain, son of Thror, rightful heir to the throne of the ancient Dwarvish kingdom of Erebor in J.R.R. Tolkien's Middle Earth.

Your people were driven from your homeland by the evil dragon Smaug, but now, after a lifetime in exile, you have traveled hundreds of miles with a group of 13 friends to reclaim your rightful title of "King Under the Mountain."

You have faced orcs, trolls and even rock giants, but now your are standing at the threshold of the secret door leading to a hidden passageway into the heart of the Lonely Mountain.

You recall the ancient prophesy, "Stand by the grey stone when the thrush knocks, and the setting sun with the last light of Durin's Day will shine upon the key-hole."

You reach into your pocket but where is the ancient Key to Erebor?

Dang it, it slipped between the couch cushions back in Rivendell!

Never mind, you can just 3D print a new one.

Warner Bros. and Microsoft are releasing a free 3D printing blueprint file of the movie prop on Dec. 13th, to correspond with the opening of "The Hobbit: The Desolation of Smaug."

"We're incredibly excited about this integrated partnership opportunity," Danni Murray, Director of Media and Marketing Partnerships, Warner Bros UK and Ireland, said. "We asked Microsoft to come up with a solution that challenged the previous conventions around what was possible with its display offering and we're confident this interactive campaign will excite and engage fans as they journey into the second film in the trilogy."

The blueprint will be offered within the Ads-in-Apps creative. Fans can download the file from the ad and use a 3D printer to create their very own keepsake.

The ad campaign will run across Windows 8, MSN and Xbox 360 for an "interactive deep-dive" into the film with information about characters, events and artifacts, actor bios, behind-the-scenes videos and more.