Hurrem Sultan Hamami is a 16th-century Ottoman bathhouse between Hagia Sophia and the Blue Mosque. It was designed by Mimar Sinan for Hurrem Sultan, wife of Suleiman the Magnificent, on a site associated with earlier Byzantine baths.
Today it operates as an upmarket hamam rather than a simple public bath. Even if you do not book a treatment, the building belongs on a Sultanahmet architecture walk.