Some sell for more than $3.5 million. Only 700 of them exist, and they're stored in vaults, frequently stolen, and often counterfeited.
The object in question? Stradivarius violins, constructed by famed Italian instrument-maker Antonio Stradivari between 1680 and 1720. Treasured for possessing sublime acoustic properties, these rare instruments have spawned dozens of theories attempting to explain their legendary tone, and luthiers—makers of stringed instruments—are still trying to reproduce it.