Discover the world's 10 longest railway tunnels, from the Gotthard Base Tunnel to the Channel Tunnel, showcasing impressive ...

Located in Spain, it comprises two parallel tube tunnels, each 28.4 km long and 8.5 metres wide, and passes through the Sierra de Guadarrama mountain range.

In this long exposure photo, a streak appears in the sky during the annual Perseid meteor shower at the Guadarrama mountains, near Madrid, in the early hours of Aug. 12, 2016. (AP photo) ...

From the rooftops of Madrid to the stone steps and peaks of the nearby Sierra de Guadarrama ... Country ranges from the dry plains of popular imagination to varied ecosystems of mountains, forests ...