Istanbul has a good and cheap public transport system. Buy a pre-paid 'Istanbul Kart' for easy access to the metro, ferries, buses, trams and funiculars. One card is enough for the whole family as you only swipe on entry. The metro now runs under the Bosphorus so it easy to get to Üsküdar and Kadıköy. Take the ferry from Eminönü to Kadıköy for fabulous skyline views back to the Mosques.