Kunstmuseum Celle Lower Saxony & Bremen

Billed as the world's first '24-hour art gallery', Celle's sexy cubed Kunstmuseum isn't actually open around the clock. During regular opening hours, you can admire the indoor collection of modern art, including the illuminated Light Room by Otto Piene. As night descends, the ‘nocturnal museum’ glows and oozes different colours as the actual building morphs into an artwork to be observed, with light and a few sounds.