Pressure Valves on an old Steam Boiler in the basement of the Old Mint (San Francisco)

Built in 1874 during the gold rush, the Old Mint was once the busiest mint in the United States. One of the last government buildings constructed in the Greek Revival style, it is also the city's oldest stone buildings. The mint operations were moved to a new facility in 1933.

The Old Mint has been closed and abandoned since 1993, threatened by demolition until the federal government transfered the building ownership to the city of San Francisco in 2003.