Madrid's main railway station has a secret: the original 1892 iron-and-glass concourse, designed by Alberto del Palacio (better known for the Vizcaya Bridge in Bilbao), was repurposed in 1992 into an indoor tropical botanical garden — 4,000 square metres of palms, ficuses, ferns, banana trees, and a pond full of turtles, all under the soaring Belle Époque iron roof.
You can walk through it for free, even if you are not taking a train. The setting — vines climbing the cast-iron columns, sunlight filtering down through the original lantern, the bustle of travellers eating ice cream on the benches — is one of the most pleasantly unexpected interiors in Madrid. Adjacent are the modern AVE terminal and the Estación del Arte metro stop (formerly known as Atocha).