The tunnel is part of the Santander-Mediterranean railway (now mostly abandoned), and it is located between Vega de Pas in Cantabria and Pedrosa de Valdeporres in Burgos. It is 6.976 m. long, and it goes under the mountain pass of Estacas de Trueba. For a long time it was the longest tunnel in Spain with all its length inside the country, until the Barcelona tunnel (in the Saragossa - Barcelona railway) surpassed it. Nowadays the Engaña tunnel looks small compared to the twin Guadarrama tunnels, with over 28 Km. each. Anyway, it is remarkable the effort required to dig the Engaña tunnel, started almost seventy years ago and with very reduced resources.
The Santander - Mediterranean railway
The construction of the tunnel started with the foundation of the two villages for the workers in 1942. Those workers were political prisoners from the Spanish Civil War. The villages, located near Vega de Pas and Pedrosa de Valdeporres, had a population of 190 and 370 respectively.
The works were firstly appointed to the Ferrocarriles y Construcciones ABC company, with a deadline of 52 months. Eventually, the section between Vega de Pas and Pedrosa de Valdeporres was not (partially) completed until 1961, 19 years after being started. The works included the villages for the workers, four tunnels and three stations. All these buildings can still be seen, although some of them are in very bad condition.
Entrance to the workers´ village of Pedrosa de Valdeporres
The village also had a church, which also served as a theater.
Next to the south entrance of the tunnel, there is this huge tower. It is a silo with a watchtower attached to it. Now the ladder to the top of the watchtower has dissapeared.
In forn of the tower we can see this power plant. There can be seen the transformer tower, and under the entrance gates the furnaces which powered the station.
The south entrance to the tunnel
Now the tunnel is in really bad condition, because of the low quality of the materials used in its construction. In 1999 there was a collapse wich made it impossible to pass through the tunnel with a vehicle, and in 2005 there was another collapse which blocked the way almost completely. In fact it is very hard to go through the tunnel on foot. Anyway, we strongly discourage entering the tunnel, because in addition of the great risk of collapse it is always flooded since the water leaks have never stopped.
But what we do reccomend is visiting the entrance itself, which is perfectly signaled. The local authoriries have tried to recover the place, creating some trekking routes. It is also frequent seeing neighbours from the nearby villages there, enjoying a walk in this privileged landscape.