The La Peña Reservoir Tunnel is a 47 meter long monotube road tunnel excavated in living limestone, dating from the early 20th century, built at the same time as the La Peña Reservoir, which was Inaugurated in 1913. For much of the same century, it was within the route of the old road from Tarragona to San Sebastián (N-240), and the main access road to the central Aragonese Pyrenees.