The basilica cistern is located in between hagia Sofia and the blue mosque! Look for the police station it is accross the street! It's a bit confusing since the cistern is underground. You will have to enter a small building that leads you underground. Pay as you enter and it was very inexpensive! I love the medusa head and the cistern ; nice picture taking inside and you can also dress like sultans and have picture taken it was cheap too if converted to dollar! Overall, it was a pleasant experience!