The station of the month: Mar de Cristal, on L4

Mar de Cristal station, in the district of Hortaleza, opened to the public on 27 April 1998, as part of the third extension in the history of this line, between Esperanza and Mar de Cristal. On that day, the Canillas station also came into service, in a neighbourhood which, like Hortaleza, had been an independent municipality of Madrid until the 1950s.

That 2.4 kilometre extension was undertaken with a tunnel boring machine and was only a foretaste of a larger project. The L4, originally conceived in 1941 as the "boulevard line" between Goya and Argüelles, was to grow even more before the end of that year on 15 December, with the entry into service of the section between San Lorenzo and Parque de Santa María.

Before that, on 24 June, Mar de Cristal had already become a key communications hub for the Madrid Metro network with the entry into service of the new line 8 to Campo de las Naciones, which in the future would be extended to the airport. This line replaced the former L8 between Fuencarral and Nuevos Ministerios, which is now part of L10.

This way, in 1998, the Metro looked to the future and brought forward its entry into the 21st century. Also in terms of design, because the Mar de Cristal station was conceived with a more functional structure than what had been built until then, with three clearly differentiated, open-plan levels, each of them visible from the other two. The use of tunnel boring machines enabled the construction of shallower stations, in this case using the method known as "cut and cover".

This superficiality made it possible to provide the Mar de Cristal station with its most characteristic and innovative element: a glass dome that allows natural light to pass from the hall to the platform. It is also a special station because of its octagonal structure and because it is clad in red.

It is fully accessible and used by some 10,000 passengers a day.