The most powerful steam locomotive on passenger express service in the heyday of Spanish steam, was the 242F, 2000 series. Their wheel arrangement: 4-8-4, was unusual in Europe, while it was more numerous in the Americas. There were only a few 4-8-4s built for the Spanish rails as by then, the world was already turning into a diesel-powered train system.
This photo was taken by the prolific Brian Stephenson from Railpictures.net. It is of the 242F 2009 pulling the La Coruna Express in May 1968. Soonafafter these pictures, most of the magnificent 242F locos were moved to the Miranda de Ebro lines for their last trips.