Pedras Salgadas Spa & Nature Park

Two treehouses on stilts float above an ancient forest in a nature reserve that was once a royal retreat, which sets the tone for this spa resort an hour from Porto. Twelve eco-houses by architect Luis Rebelo de Andrade were built to disturb as little forest as possible, while the 19th-century thermal spa was quietly refreshed by Pritzker laureate Álvaro Siza Vieira. The thermal baths do the rest.