The Hagia Sophia is a stunning piece of living history. Over the course of 1,500 years, this captivating 6th-century structure has transitioned from cathedral to mosque to museum—and is now, again, used as a mosque. The building’s beauty expertly melds the art and architecture of the Byzantine and Ottoman empires and includes a plethora of art, such as the well-preserved Christian mosaics and gilded Quranic verses that adorn the interior.

The Blue Mosque (Sultan Ahmet Camii) is located in the heart of the Sultanahmet District, opposite the Hagia Sophia. Commissioned by the youthful Sultan Ahmed I, the 17th-century marvel was completed in only seven years. Adorned with over 20,000 handcrafted tiles from the nearby city of Iznik and featuring intricate calligraphy, chandeliers, and Quranic verses, the mosque is a captivating display of artistry combined with spiritual significance.

The Topkapi Palace was the primary home of Ottoman sultans for nearly 400 years (1478–1856) and had the capacity to house up to 4,000 people. The building became a museum in 1924 and now preserves significant Muslim relics, including the Prophet Muhammad's alleged cloak and sword. Other highlights include opulent Ottoman robes, the famed Spoonmaker's Diamond, and the intricately designed harem area, which offers a glimpse into the lavish lives of the Ottoman rulers.

The 16th-century Suleymaniye Mosque, designed by the royal architect Mimar Sinan (under the direction of Sultan Suleiman the Magnificent), is situated near the Spice Bazaar, away from the tourist center—and, therefore, sees fewer tourists than other comparable sites. The Suleymaniye Mosque is the final resting place of Sultan Suleiman and his influential consort, Roxelana (Hurrem Sultan)—and of its architect, Sinan, himself.

The Istanbul City Walls, constructed in the 5th century under the direction of Emperor Theodosius II, served as a robust defensive system for over a millennium. Measuring approximately 7 miles (12 kilometers) in length, the walls once featured towers and moats. Today, many sections of the walls have been damaged beyond repair, but there are a few designated sections where you can climb a portion of the wall. The most convenient access point is near the Kariye Museum (Kariye Müzesi).

The Hagia Irene (Aya Irini), commissioned by Emperor Constantine I in the 4th century, was Constantinople’s first church. After the first version of the building was destroyed in the Nika revolt of 532 CE, Emperor Justinian I undertook its reconstruction. Today, the Hagia Irene is known not only for its architecture and history but also for its fantastic acoustics. The church also functions as a performance venue during the city’s world-renowned Istanbul Jazz Festival.

The Hippodrome of Istanbul, constructed in the 3rd-century, was a vast racetrack with an estimated seating capacity of 100,000. In addition to chariot races, the site also hosted political discussions—making it one of the city’s rare locations that welcomed royalty, politicians, and commoners alike. Eventually, the Hippodrome fell into ruin, leaving only three surviving monuments: the Obelisk of Theodosius, Serpent Column (Delphi Tripod), and Obelisk of Theodosius.

The Zeyrek Conservation Area was established to preserve earthquake-damaged Ottoman mansions and restore their lattice work, decorative wooden screens (mashrabiya), overhanging eaves, and pastel paint to their former 19th-century splendor. The area’s top landmark is the 12th-century Zeyrek Mosque (originally the Monastery of the Pantokrator), one of the city’s best-preserved Byzantine structures. Other local sights include the 4th-century Roman Valens Aqueduct, and Fatih Memorial Park.

Though the Archeological Site of Troy lies outside Istanbul’s city limits, this UNESCO World Heritage Site, near Canakkale, is a popular day trip destination. Since its founding in the Early Bronze Age (3,000 BCE), the city was rebuilt multiple times after the Trojan War. Points of interest include the symbolic location of the Trojan Horse deception, the possible former site of the Scaean Gates, and areas associated with Achilles' confrontation with Hector.