The castles, bridges and palaces overlooking the Bosporus may be impressive, but it’s the smaller yalılar (waterfront mansions) that whip many people into a photo frenzy on a Bosporus cruise. These ornate multimillion-dollar Ottoman mansions are hot properties, with prices for prime estates starting at $20 million. Buying one is no easy feat. Sales are conducted in the utmost secrecy as many high-profile owners seek to avoid gossip and prefer anonymity.