Situated on the Douro river, The Rebello hotel in Porto features 103 rooms, a full-service restaurant, two bars, and a luxurious yet unfussy spa. But it’s the design, of course, that we’re most taken with. Outside, local architecture firm Metrourbe transformed a disused, 19th-century factory for kitchen utensils into four thoroughly modernized yet character-rich buildings, two of which were newly constructed to connect the original stone structures. Inside, Spanish designer and founder of…