I remember the first time I went to Atocha during a school trip to Madrid, we went to the station only to see the lovely garden in the center of the building. It is very relaxing, with the water almost like foam and falling from the roof every now and then to keep a given level of humidity for the plants. It was incredible how quiet the station was compared to the other big railway stations in European capitals.
Atocha Railway station is Madrid's main station. It is now divided in three parts: one for the suburban trains (cercanías in Spanish), the Puerta de Atocha station (from where the fast trains go) and the Atocha Renfe one for the other trains. The original building is the one in the front, recently restored. A fire destroyed it partially.