While visiting Guanajuato we went on a walking tour and along the way we had to walk through a couple different tunnels. The city is built between a series of large hills and given its mining past, and present as well, the shortest and easiest way to connect the city as it grew was through the use of tunnels. They were designed for both vehicular and pedestrian traffic and because the ground is stone the stonework employed is quite impressive. As you can see here, there are stairs leading in and out so that people on foot don't have to go too far out of their way when they employ these subterranean shortcuts.
Canon 1D X, Canon 16-35/f2.8L Mark II
35mm, f4, merged layers of 1/125 and 1/30 sec @ 250 ISO