Mysteries, military bases & monks: Going deeper on ex Soviet Union underground

Many interesting things are hidden under the ground. In Odessa, Ukraine, man-made caves are scattered across the region and are 2,500 km long. These so-called catacombs were home to partisan bases during World War II. In Vladivostok - the main Russian military naval base in the Far East - engineers built a fortress at the beginning of the 20th century. Also, the largest underground Russian church is hidden in Penza.