Çengelköy

This attractive neighbourhood was home to a large Christian and Jewish population until some decades ago and still has a number of sights like two synagogues, some churches among which the Armenian Surp Krikor Lusavoriç, dozens of wooden houses and a Jewish and Christian cemetery.

Vast underground cistern built by Justinian in 532 to store the city's water, the largest and best-known of the hundreds constructed. It's a cathedral-like space with 336 richly decorated columns. Time was you explored in a little rowing boat, but tourist numbers have soared and water levels have dropped, so now you follow a boardwalk, with lights, piped music and art installations. It's sometimes a film location, and stages concerts. But the crowds rob it of atmosphere and you might prefer to seek out one of the less-visited cisterns.

Built 1748-55, this launched the style we call Ottoman Baroque, with its grand central dome and pencil-thin minarets. It was copied throughout their empire and is replicated in new mosques even today. The name means "light of the Ottomans," and the interior uses light powdery decor, bathed with much more natural light than its gloomier classical predecessors. The complex also has a madrasa and the imaret (public soup kitchen).

The third and grandest of the churches on this site, completed in 537 AD. The 30-m diameter dome covers what was for over 1000 years the largest enclosed space in the world, only surpassed in 1520 by Seville cathedral. It used "pendentive" architecture to throw the dome's weight onto four stout pillars, a design that inspired many Eastern Orthodox churches and Ottoman mosques. It became a mosque after the Ottoman conquest in 1453, remaining so until 1931. It was then a museum until 2020 when it was again proclaimed a mosque. That means you must work around prayer times and dress appropriately.

The only active Ashkenazi Synagogue open to visits and prayers.

One of the icons of the city is also called the Leander's Tower, on a Bosphorus islet off Salacak. The local myth ascribes its name to a princess, whose father wanted to protect her in this offshore tower from a prophecy that she would be killed by a snakebite on her birthday, but the snake found its way inside a basket of fruits — ironically a birthday present from her father — and you've probably already guessed the rest of the story. In actual timeline, it served as a defensive structure (there was a wall connecting it to the Asian mainland, and the Byzantines used to stretch a chain from here to the European mainland across the mouth of the Bosphorus to shut it to adversary shipping in times of conflict, but they didn't during the final Ottoman siege in 1453), as a customs and quarantine station, as a lighthouse, as a warehouse of various sorts of goods, and as a high-end restaurant before the last restoration finished in 2023 dedicated it as a museum. There is a light show viewable from the mainland every day at 21:00.

A contemporary art museum in a building converted from an old power plant: 1914-built and coal-fired, this was the oldest in Istanbul and the Ottoman Empire. Part of the plant was kept in almost exact original condition and now serves as the "Energy Museum".

Among the exhibition of this museum are five thousand pieces from the Ottoman era through WWII, with the most prominent piece possibly being the huge chain that the Byzantines stretched across the mouth of the Golden Horn to keep out the Sultan's navy in 1453 during the siege of Constantinople. In the yard of the museum, the Janissary Band (Mehter Takımı), the world’s oldest military band gives concerts of march music in traditional uniforms each afternoon, at 15:00.

Although not at the size of Hagia Sophia, this is the largest active church in Turkey. It’s directly on Istiklal St, but somewhat hidden from view by its yard portal. Catholic Masses in Italian, Turkish, and English (in different days of the week).

A former synagogue, the museum's exhibit details how the cultures mixed with and influenced each other in the past 500+ years since the Spanish expulsion.

Built in the early 5th century as a monastery dedicated to Saint Andrew the Apostle, in 766 it was the burial place of Saint Andrew of Crete and was later re-dedicated to him. It was rebuilt in the late 9th century and again in the 13th, then around 1490 converted into a mosque. From the 16th century it was occupied by the Dervishes, when the legend arose that a chain hung to a cypress tree in the courtyard was a truth diviner. The chain was swung between rival witnesses and the one it hit was telling the truth. The cypress stump is still standing.

Built circa 1200 as the Eastern Orthodox Theotokos Kyriotissa Church, after the Ottoman conquest it was handed over to the Qalandari, a Sufi sect. In the mid-18th century it was converted to a Sunni mosque, and its mosaics were plastered over. The original appearance was restored in the 1970s.

Built in first half of the 15th century, this is the large medieval castle under the Second Bosphorus Bridge. Its former name Boğazkesen (Turkish)/Laimokopia (Greek) means both "strait-blocker" and "throat-cutter" in both languages and denotes the reason of its building—to shut the supply routes from the Black Sea in the north into the slowly falling apart Byzantine Empire through the Bosphorus. Rumeli, literally "the Roman land", was the name of the European half of the Ottoman Empire, and as is usual with some other structures and villages along the Bosphorus, used as a prefix to differentiate Rumeli Hisarı from its counterpart in the Asian Side, the much smaller Anadolu Hisarı just across the Bosphorus.

A remarkable Bulgarian Orthodox church better known as Demir Kilise, "Iron Church", as it's a cast iron prefab. The Bulgarians split from the Greek Orthodox and established their own wooden church in 1870, which burned down. The ground was too weak for a masonry or concrete structure so they opted for cast iron. The sections were cast in Vienna, shipped here and assembled, to open in 1898. The church was renovated in 2018, but the archpatriarchate building across the street remains a gaunt shell.