Should you rent a car in a megacity? You should definitely do it. Not only can you explore Istanbul by car, you can also visit many great places around the city.
Sapanca Lake, a green paradise of songbirds, cherry trees, and cool spas, is only one hour and a half drive away. Two hours’ drive away is the town of Kıyıköy with an ancient Byzantine fortress, monastery, and caves where pirates used to hide. About a hundred kilometres from Istanbul is the town of Ağva with secluded beaches, green forests, and very photogenic cliffs. Half an hour away is Anadolu Lighthouse with the ancient Yoros Castle and delightful fish restaurants.
This is by no means a complete list of places of interest near Istanbul that are worth visiting by a rental car.