Have you got a Paris pied-à-terre dream? Ask Christophe Chastel. The founder of Guest Apartment Services, Chastel has been making a living for 30 years managing, and then selling, apartments on Île Saint-Louis in the middle of the Seine in central Paris.

Sandstone 17th-century buildings rise up over cobbled roads. Joggers and pre-schoolers holding parents’ hands dominate streets in the morning; tourists throng in the afternoon and into the evening; locals of decades’ standing emerge as the crowds thin, lingering against the stone walls and chatting in the mild spring evening. Jewellers, ice-cream shops, art dealers and even a historic Polish library take up space in other buildings on the island.