Turkey is a big and interesting country. There are more than two dozen good, interesting routes in Turkey – Pamukkale, Cappodokia, Turkish resorts, …. choose what you like.
I advise you to take a ride through the nearby villages, which are quite numerous near Istanbul. They do not have such crowds of tourists and here you can fully experience the atmosphere in which the locals live, as well as get to know their culture and values better.