Musée Horta Brussels

The typically austere exterior doesn’t give much away, but Victor Horta’s former home (designed and built 1898–1901) is an art nouveau jewel. The stairwell is the structural triumph of the house: follow the playful knots and curlicues of the banister, which become more exuberant as you ascend, ending at a tangle of swirls and glass lamps at the skylight, glazed with plain and citrus-coloured glass.