Sweden's frigid and lengthy winter nights could easily deter potential visitors—unless, of course, you're seeking a rare modern luxury: an uninterrupted, rejuvenating night's sleep. A ferry glides steadily through the frozen Baltic Sea, its route meandering past the eastern expanses of Sweden's archipelago. Rust-red cottages line jetties adorned with names like Skarpö, Hjälmö, and Gällnö, each hinting at its insular identity with the Swedish suffix “Ö,” meaning island. The