İstanbul is a must and not only because of its historical importance, but also for its diverse art, fashion, food and nightlife alternatives. The Blue Mosque, Hagia Sophia, Basilica Cistern, Topkapi Palace, Grand Bazaar, Spice Bazaar, Galata Bridge, Galata Tower, Beyoglu/Taksim, Nisantasi, cruises along the Bosphorus, an excursion to Princes’ Islands and the Istanbul Modern or Archaeology museums are the main tourist attractions.
Cappadocia is on everyone’s list of must-sees: it’s an incredible volcanic moonscape filled with lavishly decorated cave churches, homes, workshops and even cave hotels. You can even fly above the moonscape in a hot-air balloon.
Pamukkale, meaning “cotton castle” in Turkish, is recognized as a World Heritage Site and is a very popular tourist destination as well. The city contains hot springs and travertine (terraces of carbonate minerals left by the flowing water.) People have bathed in its pools for thousands of years.
The Turquoise Coast (also known as the Turkish Riviera) is the combination of a favorable climate, a warm sea, more than a thousand kilometers of shoreline along the Aegean and Mediterranean waters and abundant natural and archeological points of interest. I would suggest doing a multi-day cruise in this area.