Palau Güell sits just off La Rambla in the Raval district, and it has always been an act of deliberate provocation. When Gaudí completed it in 1888, the surrounding neighbourhood was one of Barcelona's most disreputable. Every other wealthy family was decamping to the new Eixample. Eusebi Güell, the industrialist who commissioned it, planted his flag here anyway, wanting a townhouse grand enough for ten children and lavish enough to host the city's elite.

It's one of Gaudí's most understated buildings, which says a great deal given his other work. But look closer: the cast-iron gates, the parabolic arches, the main hall rising into a lantern-lit dome. This was his laboratory, the place where his vocabulary was first assembled.

VoiceMap's El Raval and Gothic Quarter tour uses Palau Güell to trace Gaudí's early creative partnership with Güell, explaining what drew the architect to this unfashionable neighbourhood and how the building's restrained exterior conceals the extraordinary experiments within.