Tate Modern

This building used to burn oil to power London. Now it burns through over five million visitors a year who come to see some of the most important modern and contemporary art in the world. The conversion of Bankside Power Station into Tate Modern is one of the great reinvention stories in architecture — a place that generated electricity for thirty years now generates conversation.

Sir Giles Gilbert Scott designed the original power station, the same architect behind the red telephone box and Battersea Power Station. The building operated from 1947 to 1981, when rising oil prices made it uneconomical. Swiss architects Herzog & de Meuron won the competition to convert it, and their genius was in what they didn't change. The £134 million transformation preserved the cathedral-like Turbine Hall — 155 metres long and 35 metres high — as a single overwhelming space for large-scale art installations.

Since the museum opened in May 2000, the Turbine Hall has hosted some of the most ambitious art commissions of the 21st century. Olafur Eliasson's artificial sun drew two million visitors in 2003. Ai Weiwei filled the floor with 100 million hand-painted porcelain sunflower seeds. Each October-to-March commission turns this industrial cathedral into something utterly unpredictable.

The Switch House extension, now called the Blavatnik Building, opened in 2016, adding ten floors of gallery space in a perforated brick tower. From its viewing terrace on the tenth floor you get panoramic views across the Thames to St Paul's — the power station staring across the river at the cathedral, industry facing religion, both of them reimagined.