Casa Labra has been serving fried cod on Calle Tetuán, just off Puerta del Sol, since 1860. It also happens to be the birthplace of Spain's oldest political party. On 2 May 1879, twenty-five workers, mostly typographers, crowded into a back room here and secretly founded the PSOE, the Spanish Socialist Workers' Party. A bronze plaque on the facade marks the occasion, though you could easily miss it above the queue for cod croquettes.

The interior is wonderfully unchanged: zinc counter, dark wood panelling, blue-and-white tiles. You order your food at one window, your drink at the bar, and eat standing up. The croquetas de bacalao have barely changed in over 160 years.

VoiceMap's self-guided audio tours trace the connections between Casa Labra, Hemingway, Orson Welles and Madrid's tapas traditions, explaining why Toledo red wine here is aged in clay rather than French oak.