sentences:  AVE trains also arrive to Segovia, Valladolid, Zamora and León.Already connected by tunnels used by conventional rail lines, a tunnel link connecting the Atocha and Chamartín stations with high-speed rail services is finished but, as of August 2019, yet to be inaugurated.Serving the city's population of some six million, the Madrid Metro is one of the most extensive and fastest-growing metro networks in the world.