Railway Tunnel No. 3 of the Sierra Greenway Nature Trail. Located 505 meters from the previous tunnel, it is 70 meters long and has no artificial lighting, so a flashlight is recommended. This tunnel passes through an outcrop of marl and sandstone.
The tunnels in this railway section were constructed using shoring (supporting the excavation) with wooden beams and props, followed by formwork for the concrete slab that supports the tunnel. The tunnel entrance is finished with hewn limestone from a quarry located opposite Zaframagón.