This Tunnel is the best example of what a mine looks like tunneled.  The passageway measures 1.9 km (1.1 mi) long, and operates today as the only entrance to Real de Catorce. It was built during the times of Porfirio Diaz by Vicente Irizar Arostegui, who originated from Ogarrio, Spain, just before the end of the silver boom in this area. This access facilitated the movement of minerals for the benefit of the estates of Potrero, and Matehuala Cedral. Along the Ogarrio tunnel, numerous entrances (already covered) can be seen, that shortened the distance to other mines such as Santa Ana, El Refugio, Boqueiro and Ave Maria. Each year on April 2 is the Festival of Ogarrio, which marks the commemoration of the official opening of the passage. Moreover, during the Festivals of St. Francis of Assisi (beginning in September and ending in October), the tunnel closes its access to foreign cars and buses. The high season and holiday periods and are not exempt from the tunnel being closed to avoid congestion within the town, which is quite small. There is a fee to cross the Ogarrio Tunnel.  And, it has only a single lane that permits one car to cross at a time, so traffic is facilitated by guards that radio to the other side to coordinate the traffic. After 11:00 pm, there are no guards so cars must pass at their own risk.

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