A National Geographic journalist, while on assignment for the journal, was given a tour of the vast Paris underground, a maze of structures excavated over the years at various levels under the surface of the Earth. It consists of old crypts, used and unused sewer lines, metro train tunnels, the empty quarries from which much of the stone used to build the city was extracted, and heavily fortified vaults under banks and museums. The journalist and author of the source article, Neil Shae, and his colleague, photographer, Stephen Alvarez, were taken into the vault under the Banque de France and shown the French national gold reserves which are kept there in piles and piles of gold bars, each valued at around $500,000.

Geographic reference: France
Year: 2010
Market size: Approximately 2,600 tons.
Based on the price of gold on the international market on January 28, 2011, the approximate value of the gold bars under the Banque de France is $120.1 billion.
Source: “Under Paris,” National Geographic, February 2011, page 124. The image of gold bars we use here comes from a Banque de France Annual Report, available online here.
Original source: Banque de France