Kocataş Mansions, İstanbul

Two Ottoman-era mansions in upscale Sarıyer, far enough up the Bosphorus that the hotel runs its own boat to get you back to the city. The 45 rooms and suites are generous in size, blending contemporary design with the bones of the original buildings, and the spa is very much the point. There's also a Turkish restaurant, a Latin-Asian bar, and an all-day lounge for when the boat schedule feels too ambitious.