Istanbul’s a definite, and I’d try to give it at least three days. Then you could head down the coast to Selçuk for the amazing ancient city of Ephesus (Efes in Turkish) before hitting the Mediterranean coast. Kaş would be my choice, though do try to squeeze in a visit to beautiful Butterfly Valley, where you’ll likely be sleeping in a tent (provided) on the beach. Finish off by heading east into Cappadocia for its ‘fairy chimneys’ and underground cities. I reckon you can hit these four or five destinations in two weeks, and it’ll give you a real sense of the country’s incredible diversity.