Very interesting photo tour! Thanks for sharing. I´ve liked it.
In Madrid there´s an old subway station, Chamberí, at line 1, which has been recovered and actually works as a museum of metro. It preserves the old ceramic ads in the walls. It´s located between two metro stations, Bilbao and Iglesia, and you can see trains when they go through the station (there´re crystal sceens to avoid accidents). This station was opened in 1919 and closed in 1966. The visit is free.
I´ll try someday to show pictures about this metro museum.
Congrats and greetings from Madrid, Spain!