Casa Milà (La Pedrera)

Described variously as rising dough, molten lava and a stone lung, the last secular building designed by Antoni Gaudí, the Casa Milà (popularly known as La Pedrera, 'the stone quarry') has no straight lines. It is a stupendous and daring feat of architecture, and the culmination of the architect's experimental attempts to recreate natural forms with bricks and mortar (not to mention ceramics and even smashed-up cava bottles). Now a UNESCO World Heritage Site, it appears to have been washed up on shore, its marine feel complemented by collaborator Josep Maria Jujol's tangled balconies, doors of twisted kelp ribbon, sea-foamy ceilings and interior patios as blue as a mermaid's cave.

When it was completed in 1912, it was so far ahead of its time that the woman who financed it as her dream home, Roser Segimon, became the laughing stock of the city - hence the 'stone quarry' tag. Its rippling façade led local painter Santiago Rusiñol to quip that a snake would be a better pet than a dog for the inhabitants. But La Pedrera has become one of Barcelona's best-loved buildings, and is adored by architects for its extraordinary structure: it is supported entirely by pillars, without a single master wall, allowing the vast, asymmetrical windows of the façade to invite in great swathes of natural light.

There are three exhibition spaces. The first-floor art gallery hosts shows of eminent artists, while the upstairs space is dedicated to giving visitors a finer appreciation of Gaudí: accompanied by an audio guide (included in the admission price) you can visit a reconstructed Modernista flat on the fourth floor, with a sumptuous bedroom suite by Gaspar Homar, while the attic, framed by parabolic arches worthy of a Gothic cathedral, holds a museum offering an insightful overview of Gaudí's career. Best of all is the chance to stroll on the roof of the building amid its trencadís-covered ventilation shafts: their heads are shaped like the helmets of medieval knights, which led the poet Pere Gimferrer to dub the spot 'the garden of warriors'.