Underneath the south eastern suburbs of Greater London are 22 miles of man-made tunnels which were created for the mining of flint and chalk and date as far back as 1250. The mines, now known as the Chislehurst Caves, are a popular tourist attraction for many reasons including its use as an air-raid shelter for 15,000 people during the war and its more recent status as a popular music concert venue. The team, joined by guest medium Brian Shepherd, spend two nights investigating purported ghostly phenomena throughout this 'underground city'.