Calle de Olíd, Trafalgar, Chamberí, Madrid - and a puzzle to me.

The yellow fronted building has an old METRO logo above the door. This looks like an old workshop and although it is only about 200 metres from where I know Line 2 runs, there is no obvious sidings area nor obvious route for trains to take (and line 2 was constructed not all that far underground). The streets were all solidly built up long before the metro came through (or rather below) here! Perhaps some sidings were intended but not built, leaving the workshop high and dry. It is also quite possible that it might be some kind of electricity substation. I don't know and can't seem to find out. I have books on the Madrid Metro (how sad is that!).
Having said that, I do like the building and the street.
24 HOURS LATER AND I HAVE THE ANSWER. IT IS AN ELECTRICITY SUBSTATION, one of two that served line 2 in the early days!