3. Metro-2, Moscow
Metro-2 in Moscow, Russia is the informal name for a purported secret underground metro system which parallels the public Moscow Metro. The system was supposedly built, or at least started, during the time of Joseph Stalin and was codenamed D-6 by the KGB. It is supposedly still operated by the Main Directorate of Special Programs and the Ministry of Defense.
The length of Metro-2 is rumoured to exceed that of the public Metro. It is said to have four lines that lie 50 to 200m deep. It is said to connect the Kremlin with the Federal Security Service (FSB) headquarters, the government airport at Vnukovo-2, and an underground town at Ramenki, in addition to other locations of national importance.
In 1994, the leader of an urban exploration group, the Diggers of the Underground Planet, claimed to have found an entrance to this underground system.
Sadly, all available information is speculative and unsupported by documentation such as photographs. Also, there are narratives told by people who say that they helped build Metro-2, and urban spelunkers claim to have “seen” Metro-2, but there are no explicit “firsthand” accounts.