(FORTUNE Magazine) – As a provider of electricity, London's Bankside Power Station was a flop. First fired up in 1963, it shut down 18 years later because its power source, oil, was too expensive. Designed by Giles Gilbert Scott--the man behind the red British telephone booth--the hulking building was of interest only to architecture buffs and movie-location scouts (parts of Ian McKellen's Richard III and Sly Stallone's Judge Dredd were filmed inside). As recently as six years ago, it was headed for demolition.

Fate intervened, in the form of an expansionist museum. Bankside Power Station is getting a second lease on life as the Tate Gallery of Modern Art (opening May 12). The old Tate, housed in a former prison near Parliament, will live on as the Tate Britain. And the new Tate Modern, just across the Thames from the City, will join the not very deep ranks of the world's great modern art museums.

It's a strange, wonderful place. The power station was divided from south to north into a Switch House, Turbine Hall, and Boiler House. The Switch House is still packed with loudly humming transformers. The Turbine Hall is now a vast, unheated entrance space with a few big Louise Bourgeois sculptures. And all the Matisses, Picassos, Rothkos, and the like can be found in 150,000 square feet of galleries carved out of the Boiler House, which has been extended on top with a glass structure called the Light Beam, featuring a top-floor cafe with some of the grandest views in London.

--JUSTIN FOX

Tate Gallery of Modern Art Bankside, London SE1 9TG; 011-44-207-887-8008. Admission is free.