There are rare timepieces that hit the auction block, but this Tank Louis Cartier Skeleton is about as exclusive as it gets. The singular version was custom-made for a private client back in 2007. The watch is based on the Tank Louis Cartier Noctambule that was only made form 2004 to 2006. The watch showcases a skeletonized face and movement set within the classic Cartier tank case and forged in platinum. The face shows off the hand-wound 9610MC skeletonized caliber, thin blued Breguet-style hands, and luminous bridges. It’s paired with a black alligator strap. The watch garnered twice as much as its projected winning bid, which makes sense given the fact that it is the only one in the world.