Entrance to the mines is restricted. The portion open to the public (the catacombs) is only a small part of an extensive network of tunnels, which spans around  in length and criss-cross large sections of the city.
Access to the mines is restricted. The portion available for public exploration (the catacombs) represents only a minor segment of an extensive network of tunnels, which covers around  in length and intersects various parts of the urban landscape.