During the reign of Stalin, a secret system of underground transport was built known as Metro-2. This mysterious metro system supposedly connects administrative institutions like Kremlin, Vnukovo-2 airport and General Staff Academy. It is reported that the tunnels also include apartaments and technical rooms. Since the system was not available for outsiders, it is believed to be a secret escape tunnel for high-level officials during war. Moscow metro administration denies the existence of these tunnels, yet back in 1994 an urban exploration group claim to have found the entrance to the underground system. Now, only one out of four lines is confirmed to exist, and that is the line D6. The access to this place is strictly forbidden for outsiders and it can only be entered with a special pass.