Answer: Wine

New York City, due to its vast size and age, is home to more than a few architectural surprises and secrets. The iconic Brooklyn Bridge, linking Manhattan and Brooklyn across the East River, is no exception. Deep beneath the bridge’s anchorages on both shores, you’ll find numerous passageways and vaults.

Why build passageways and vaults into a bridge? Constructed over fourteen years (beginning in 1869), the bridge cost 15.5 million dollars (approximately $396,614,851 when adjusted to today’s dollars) with the architects and city of New York creatively putting the bridge to use to help offset the cost (the vaults were opened for use in 1876).

The vaults, thanks to their depth and stone construction, maintained a perfect 60 °F (16 °C). Wine importers and upscale restaurants around the city were more than happy to pay a premium to rent the vaults in order to protect their expensive wine and champagne collections. In the days before electric refrigeration and air conditioning, the vaults were a perfect way to protect wine against temperature fluctuations and spoilage.

Today, the vaults are no longer used for wine storage, either sitting vacant or housing far less glamorous things like piles of maintenance supplies for the crews that maintain the bridge.