Istanbul (Turkish: İstanbul, historically Byzantium and later Constantinople) is Turkey's most populous city, and its cultural and financial center. The city covers 25 districts of the Istanbul province. It is located at 41° N 29° E, on the Bosphorus strait, and encompasses the natural harbor known as the Golden Horn, in the northwest of the country. It extends both on the European (Thrace) and on the Asian (Anatolia) side of the Bosphorus, and is thereby the only metropolis in the world which is situated on two continents. In its long history, Istanbul (Constantinople) served as the capital city of the Roman Empire (330-395), the Byzantine Empire (395-1204 and 1261-1453), the Latin Empire (1204-1261), and the Ottoman Empire (1453-1922). The city was chosen as joint European Capital of Culture for 2010. The "Historic Areas of Istanbul" were added to the UNESCO World Heritage List in 1985.

The Bosphorus Bridge, also called the First Bosphorus Bridge (Turkish: Boğaziçi Koprüsü or 1. Boğaziçi Koprüsü ) is a bridge in Istanbul, Turkey spanning the Bosphorus strait (Turkish: Boğaziçi). The bridge is located between Ortaköy (European side) and Beylerbeyi (Asian side). It is a gravity anchored suspension bridge with steel pylons and inclined hangers. The aerodynamic deck is hanging on zigzag steel cables. It is 1,560 m long with a deck width of 39 m. The distance between the towers (main span) is 1,074 m (World rank: 13th) and their height over road level is 105 m. The clearance of the bridge from sea level is 64 m. It was the 4th longest suspension bridge in the world when completed in 1973, and the longest outside the United States of America.

Maiden's Tower (Turkish: Kız Kulesi), also known in the ancient Greek and medieval Byzantine periods as Leander's Tower (Tower of Leandros), sits on a small islet located in the Bosphorus strait off the coast of Üsküdar in Istanbul, Turkey.

Maiden's Tower was first built by the ancient Athenian general Alcibiades in 408 BC to control the movements of the Persian ships in the Bosphorus strait. Back then the tower was located between the ancient cities of Byzantion and Chalcedon. The tower was later enlarged and rebuilt as a fortress by the Byzantine emperor Alexius Comnenus in 1110 AD, and was rebuilt and restored several times by the Ottoman Turks, most significantly in 1509 and 1763. The most recent facelift was made in 1998. Steel supports were added around the ancient tower as a precaution after the 17 August 1999 earthquake.

Used as a lighthouse for centuries, the interior of the tower has been transformed into a popular café and restaurant, with an excellent view of the former Roman, Byzantine and Ottoman capital. Private boats make trips to the tower several times a day.

The Galata Tower (Turkish: Galata Kulesi), also called Christea Turris (Tower of Christ) by the Genoese and Megalos Pyrgos (The Great Tower) by the Byzantines, is located in Istanbul, Turkey, to the north of the Golden Horn. One of the city's most striking landmarks, it is a huge, cone-capped cylinder that dominates the skyline on the Galata side of the Golden Horn.

The Galata Tower was built as Christea Turris in 1348 during an expansion of the Genoese colony in Constantinople. It was the apex of the fortifications surrounding the Genoese citadel of Galata. The current tower should not be confused with the old Tower of Galata, an original Byzantine tower, named Megalos Pyrgos, which controlled the northern end of the massive sea chain that closed the entrance of the Golden Horn. This tower was on a different site and was largely destroyed during the Fourth Crusade in 1204.

The 66.90 m tower (62.59 m without the ornament on top) was the city's tallest structure when built. In 1638, Hezarfen Ahmet Çelebi flew as an early aviator using artificial wings from this tower over the Bosphorus to the slopes of Üsküdar on the Anatolian side.

Ortaköy Mosque, officially the Büyük Mecidiye Camii (Grand Imperial Mosque of Sultan Abdülmecid) in İstanbul, is situated at the waterside of the Ortaköy pier square, one of the most popular locations on the Bosphorus.

The original Ortaköy Mosque was built in the 18th century. The current mosque, which was erected in its place, was ordered by Sultan Abdülmecid and built between 1854 and 1856. Its architects were Armenian father and son Garabet Amira Balyan and Nigoğayos Balyan, who designed it in Neo-Baroque style.

The wide, high windows let the ever-changing light reflections of the Bosphorus shine in the mosque.

Rumeli hisarı is a fortress located in Istanbul, Turkey on a hill at the European side of the Bosporus just north of the Bebek district; giving the name of the quarter around it. It was built by the Ottoman Sultan Mehmed II between 1451 and 1452, before he conquered Constantinople. The three great towers were named after three of Mehmed II's vezirs, Sadrazam Candarlı Halil Pasha, who built the big tower next to the gate, Zağanos Pasha, who built the south tower, and Sarıca Pasha, who built the north tower.

Ordered by President Celal Bayar in 1953, the neighborhood was removed and an extensive restoration work began on May 16, 1955, which lasted until May 29, 1958. Rumelihisarı is since 1960 a museum and an open-air theater for various concerts at festivals during the summer months. The Fatih Sultan Mehmet Bridge which spans over the Bosporus is located close to the fortress, to the north.

Rumelihisarı as an open-air museum is open to public every day except Wednesdays from 9:00 to 16:30.

Hagia Sophia, Holy Wisdom, Turkish Ayasofya) is a former patriarchal basilica, later a mosque, now a museum, in Istanbul, Turkey. Famous in particular for its massive dome, it is considered the epitome of Byzantine architecture and one of the most beautiful buildings in the world. It was the largest cathedral in the world for nearly a thousand years, until the completion of the Medieval Seville Cathedral in 1520.

The current building was originally constructed as a church between 532 and 537 on the orders of the Byzantine Emperor Justinian, and was in fact the third Church of the Holy Wisdom to occupy the site (the previous two had both been destroyed by riots). It was designed by two architects, Isidore of Miletus and Anthemius of Tralles. The Church contained a large collection of holy relics and featured, among other things, a 50-foot (15 m) silver iconostasis. It was the patriarchal church of the Patriarch of Constantinople and the religious focus point of the Orthodox Byzantine Empire for nearly 1000 years.

In 1453, Constantinople was conquered by the Ottoman Turks and Sultan Mehmed II ordered the building to be converted into a mosque. The bells, altar, iconostasis, and sacrificial vessels were removed, and many of the mosaics were eventually plastered over. The Islamic features - such as the four minarets outside, the mihrab and minbar - were added over the course of its history under the Ottomans. It remained as a mosque until 1935, when it was converted into a museum by the secular Republic of Turkey.

For almost 500 years the principal mosque of Istanbul, Hagia Sophia served as a model for many of the Ottoman mosques such as the Sultan Ahmed Mosque (Blue Mosque of Istanbul), the Şehzade Mosque, the Süleymaniye Mosque, and the Rüstem Pasha Mosque.

İstanbul Aquarium , A bit of a cheat, this one, since it isn’t really a museum at all. On the other hand the new İstanbul Aquarium in Florya goes in for a bit of cheating itself since alongside the huge tanks of fish on display it also devotes lots of wall space to the stories of the Panama and Suez Canals. Pride of place is a giant tank ringed with replicas of Bosporus buildings although many people will probably leave with a more vivid recollection of the steamy room devoted to the Amazon rainforest and to a tank of piranhas that look nowhere near as fearful as their reputation might suggest.