Ah, the eternal Istanbul conundrum: a pummeling at a historic, no-frills hammam such as Cağaloğlu, or a luxurious steam at a modern hotel spa. Ayasofya Hürrem Sultan Hamami (1 Cankurtaran Mahallesi Bab-i Hümayun Cad.; 90-212/517-3535; treatments from $90), which recently opened between the Blue Mosque and Hagia Sophia, offers the best of both worlds. The double-domed structure returns to its original incarnation—it was built as a bathhouse in 1556 by Mimar Sinan. Now, it shines with 1,400 square feet of marble, gold-plated faucets, and a galleried cedar cold room under a soaring cupola. After aromatherapy and bubble massages, guests can linger in the relaxation lounge over Turkish delights while the sound of a muezzin echoes in the distance.