Underground Moscow holds many secrets. During the years of communist rule there was little investigation of the city's history and heritage. Now underground explorers, or diggers, have a mission to uncover their city's secrets. Nigel Wrench traces the history of the Russian capital and meets these subterranean explorers and archaeologists.

[Article] Saturday PM presenter Nigel Wrench (above) has covered some tough stories in his career as a journalist, from the anti-apartheid protests in 1980s South Africa to reporting from Jerusalem. He's no cissy, in other words, but he simply wasn't prepared for how unsettling it would be to record a programme in a completely black tunnel, walking through smelly water and trying to keep his balance, deep beneath the streets of Moscow. "This is the scariest thing I've ever done," he says, "I think this may be as far as I go." He does, however, spend time talking to the people called "diggers" who have gone much further These subterranean explorers are hoping to find the secret libraries of Ivan the Terrible, which are thought to contain a fabulous collection of invaluable books and scrolls from Byzantium. The current mayor of Moscow has put of lot of money into the hunt but the main discoveries so far have been what one expert refers to as "a lost empire" of secret tunnels commissioned by Stalin. As Wrench resurfaces from his own digging experience his relief is palpable: "The sky looks like I'm seeing it for the first time."