The city of Bursa on the south side of the Sea of Marmara has almost 1.8 million people, and was the first capital of the Ottoman Empire in 1326. It is the fourth most populous city in Turkey. It sits on the slopes of Mount Uludag and has more mosques and tombs than any city in Turkey. It has a lot of different architecture styles and is within a day's distance from Istanbul to visit.
It's perfectly located at the skirts of Uludag, which has the biggest ski center in Turkey and lays towards to north. In just an hour, it's possible to go to ski center as well as to the coast of Marmara sea.