Commissioned in 1740 under the Spanish Bourbons, Castillo del Príncipe — named for the son of King Charles III — is a rare horseshoe-shaped coastal fortress restored into a nine-bedroom retreat overlooking Galicia’s rugged Costa da Morte.

Set above the Somme River near Abbeville (1h40 from Paris), this 18th-century pink-brick residence is positioned atop a series of terraces with century-old greenhouses—each nearly 100 metres (328 feet) long—among the largest in private ownership in France.