This railway is an example of great frustration. The Santander-Mediterranean Railway was a late project (its concession dates back to 1924), the last major line undertaken by private capital in Spain, when at that time several hundred kilometres of the lines of the Guadalhorce Plan were already being built by the State.

The different sections of this very long line, which started in Calatayud, Aragon, and was supposed to reach the port of Santander, via Burgos and Soria, were opened at a good pace. Its planned length was 415 km but, in the end, only the 365 km that ended at Burgos’ Dosante Station could be built.

The fact that it at the remote spot of Cidad, in Burgso, was due to the challenge, which was not overcome, that it faced to the north: boring the long tunnel that would enable trains to pass under the Cantabrian divide. With 7 km planned, the La Engaña Tunnel was the longest underground railway project ever conceived in Spain. On the other hand, at the exit of the tunnel there was the not inconsiderable challenge of taking the railway down from Yera, at a height of 750 m, to sea level at the port of Santander, through rugged terrain that was extremely hostile to engineering and over a distance of less than 40 km as the crow flies.

Faced with all this, the railway company’s investors opted to put a "provisional" end to its tracks at Dosante-Cidad Station, parallel to the narrow-gauge La Robla Railway Station, thereby creating a transfer point. During the Second Republic, the State assumed the continuation of the project. Once the line was integrated into Renfe in 1941, the State continued for another 17 years in the construction of the hardest part, the tunnel, which was completed with the help of hundreds of workers, some of whom were Republican prisoners of war.

However, despite finishing the very complex and titanic underground work, in 1959 construction was stopped once and for all, when only the downhill section to Santander remained to be built. The famous World Bank report finally condemned this unfinished project to oblivion, along with other similar ones in the rest of Spain.

The rest of the railway continued to be operated by Renfe, experiencing only the loss of the section from Pedrosa to Cidad at the end of the 1970s. In any case, shortly after, and along with hundreds of other kilometres, on 1 January 1985 it was closed in its entirety, being the largest line of those closed throughout Spain all at once.