The concept of infinite blue was architect Gio Ponti’s driving inspiration when he built Parco dei Principi, his slice of 1960s modernism on a coast of faded antiquity. When it opened in 1962, the hotel was something new for ancient Sorrento: a clean-lined, contemporary edifice on the tufa-stone cliff. Inside, the bright, wide-open spaces were pared down and decorated entirely in white and blue.