Guanajuato is a mountain town carved into several very steep valleys. Because of this and the abundance of mines in the area, someone decided that the best way to provide for motor cars was to blast a bunch of wholes in the mountains. If you could take an x-ray of the Earth, Guanajuato would look more like a piece of Swiss cheese than any other city in the world.
For the film festival, during the evening after 11pm, they close down a small section and show films inside the tunnel.
In the 1st foto you can see the traffic arrow and if you look closely you can see the no "E" Estacionar, Mexican no parking signs.