The gold leaf around the window and door frames ripples, reflected in the water of the swimming pool. Elegant, spare, pristine, the Villa Empain in south Brussels seems little changed since it was built over 90 years ago. Yet this art deco masterpiece reopened only in 2010 after falling into ruin. Illegal ravers had scrawled on its marble walls and stolen its treasures, from radiator grills to a decorative fish that was the centrepiece of a fountain in the bar. Now restored to its former opulence, the villa is one of the highlights of Brussels’ year of art deco as...