Here are my top 15 things to do in Istanbul, in no particular order. I chose these not because they are popular, but because I think they are worth seeing or experiencing. Therefore, for instance, I didn’t include the world famous Blue Mosque, but suggest something different. I also draw attention to many hidden gems, often overlooked while preparing for your visit. Enjoy!
A trip to Istanbul is not complete without a Bosphorus cruise . Not only provides it a nice overview of the city, both the European and Asian shores of the famous waterway have a lot to offer – century old palaces and mansions galore.
There are several cruises you can take: a short one (to the second suspension bridge and back), a long one (all the way to the Black Sea and back), and a sunset tour in summertime.
The latter used to be my favorite, but became victim of its success. These days I prefer to take the full Bosphorus day tour, or the shorter version if you are pressed for time.
This splendid church-turned-mosque-turned-museum is among the world’s greatest architectural achievements. After years of restoration works, the Hagia Sophia (Aya Sofya) is finally scaffolding free, enabling you to absorb its splendor as it was meant to be.
Standing in the middle of the staggering spacious nave under the 43 meter wide dome 65 meters above your head defies belief – and physics for that matter. Climb up the spiral ramp to get to the gallery and gaze at the splendid Byzantine mosaics, including Christ flanked by Emperor Constantine IX and his wife Empress Zoe.
Topkapi Palace (Topkapi Sarayı) is rightfully a sight you can’t afford to miss while in Istanbul. This complex of kiosks and pavilions contained by four lush green courtyards is where generations of sultans had their principal residence for almost half a century.
Top attractions at Topkapi Palace are the Harem, an adorned ‘cage’ of the sultan’s women, the treasury storing the crown jewels and containing the famous Topkapi dagger, and the weapon’s room boosting their fine craftsmanship even when it came to making swords and bows.
Also, don’t forget to walk all the way till the end for breathtaking views of the Sea of Marmara, Bosphorus and Golden Horn.
Istanbul is not only fascinating above ground, but also underground with the Basilica Cistern (Yerebatan). This exquisite piece of Byzantine engineering is a spectacular underground cistern, once bringing drinking water with aqueducts from current Bulgaria to Istanbul.
With its dimmed light and classical music to the background sound of dripping water, some find it romantic while others experience it as slightly spooky.
Tread the walkways and watch the fish swim between the 336 columns that support the ceiling. Walk all the way to the end to see the Medusa head, placed upside down as the base of one of the columns.
People often skip the Archaeology Museum (Arkeoloji Müzesi), and that’s a pity. This is a real hidden Istanbul gem, displaying one of the world’s richest collections of classical antiquities.
Top attractions here are the marvelous sarcophagus of Alexander the Great depicting important phases of his life, the blue tiled Karaman Mihrab, the beautiful Tiled Pavilion, and the Treaty of Kadesh – the world’s earliest surviving peace treaty. Not an option with kids? Wait until the see the model Trojan Horse in the children’s section.
You can reach the Archaeology Museum by going left down the hill in Topkapi Palace’s first courtyard, or via Gülhane Park.
Museum of Turkish and Islamic Arts
The Museum of Turkish and Islamic Arts is much more exciting than the name reveals. Housed in the former palace of Ibrahim Pasa — the most talented Grand Vizier of Süleyman — and overlooking the Hippodrome, the collection has over 40.000 items on display.
Each room concentrates on a different period or area of the Islamic world, also reflecting daily Turkish life from the 8th till the 19th century. Top features are the world renowned collection of gigantic carpets hanging from the ceiling, a recreation of a Turkic nomadic tent, and the peaceful Turkish coffee house where they brew Turkish coffee  over an open fire.
Bargain hunting at Istanbul’s Grand Bazaar . Over 500 years old, but still one of the largest covered bazaars in the world. Its 60 streets contain no less than 5000 shops, 60 restaurants, 18 fountains, 12 mosques, and even a school.
This is not a tourist trap as some claim. Locals shop here every day, but odds are they’re better at bargaining than you are. The bazaar is very famous for its carpets, leather, ceramics, souvenirs and jewelry.
It’s hard not to get lost in this chaos, so try to remember where you entered before wandering around.
Instead of the iconic Blue Mosque, I prefer the less famous Süleymaniye Mosque. I think it’s the nicest and most impressive Istanbul mosque, and not invaded by thousands of tourists every day.
The Süleymaniye Mosque was designed by the famous architect Sinan for Süleyman the Magnificent, and is a great tribute to both. It’s actually much more than a place of worship. It’s a complex of buildings containing a hospital, a kitchen, a school, etc.
Don’t forget to visit the tombs of Süleyman and Roxalana behind the graveyard, the tomb of Sinan outside the complex, and eat kuru fasulye (haricot beans) in one of the many restaurants in the Alley of Addicts.
Chora Church / Kariye Museum
The Chora Church , Church of St Savior, or Kariye Museum is a bit off the beaten track, but well worth a visit. Located in Chora/Edirnekapi next to the old city walls, it is one of the most amazing religious building Istanbul has to offer.
The walls and ceilings of this church are adorned with stunning Byzantine mosaics and fabulous frescoes. Some are considered as the most significant in the Christian world.
And while you’re there, enjoy the remains of the fifth century city walls and the wooden Ottoman houses.
Dolmabahçe Palace is just fascinating. A few facts to demonstrate my point here. The palace is huge — 600 meters in length — containing no less than 285 rooms and 43 salons. It was built in 1856 by Sultan Abdüi Mecit, basically to prove that the declining Ottoman Empire was doing just fine, whereas the construction resulted in exactly the opposite.
Nevertheless, no expenses were spared, proof of which the excessive use of gold leaf, crystal and marble. Obvious key features are the Baccarat crystal staircase, the main bathroom, and the ceremonial hall with its 4.5 ton chandelier. Just seeing the latter is impressive!
After the foundation of the Turkish Republic, Atatürk adopted the palace as its home, and died there November 10, 1938 at 09:05. As a tribute, all clocks in the palace show that time.
The Galata Tower is one of the best spots in town to get a 360 panoramic view of Istanbul. On a bright day you can even spot the Princes’ Islands  from this 60 meter high tower. There is also a restaurant/cafe at the ninth floor, but feel free to skip that entirely.
Instead, walk around in the cozy streets of Galata surrounding the tower and have a drink or some food on one of the many terraces. Not only will you enjoy it much more, you’ll also get a much better deal.
Bebek and Ortaköy
Bebek  and — to a lesser extend — Ortaköy are two village by the Bosphorus worth visiting, yet lesser known among tourists.
Bebek is a lively, green, and wealthy neighborhood by the Bosphorus. It’s well known and frequently visited by locals during the weekends. It’s a local all-time favorite to have a (late) breakfast  with a stunning view followed by a nice stroll on the boardwalk, topped with a drink in one of the many cafes . Other come later, and enjoy the buzzing nightlife.
If you took a Bosphorus tour, it’s hard to miss Ortaköy. Its cozy mosque by the shore just before the first bridge stands out. Another thing that draws a lot of attention is the Sunday crafts market, as well as the many car-free cobbled stoned streets filled with restaurants and cafes.
Visit Local Markets
Turkey’s kitchen is among the richest of all, blending flavors of different continents and cultures.
All these dishes are made with fresh produce, stuff you too can buy first hand by visiting local markets in Istanbul . These town markets (pazar) can look overwhelming at first, but be assured that you’ll receive a warm welcome by stallholders. Communication may be difficult, but the experience is priceless.
Istanbul’s nightlife  can compete with the rest of the world. Whether you want to enjoy a (local) live performance while sipping on your favorite drink, attend concerts of current and past world stars, or dance the night away in open-air venues by the Bosphorus or while enjoying a rooftop 360 view, Istanbul has it all.
Getting Scrubbed in a Hamam
There is nothing better to rejuvenate your body than getting scrubbed in a hamam. Just picture this after a long day of walking: wearing nothing but a cotton cloth, first relax in a steamy room laying on hot marble, listening to the echoes of running water. Then a brisk soapy body scrub, followed by a sultan’s massage until your skin is smooth and soft.
There are several hamams available in the city. Among the oldest are the (recently renovated) Ayasofya Hürrem Sultan Hamam and Kılıç Ali Paşa Hamam. The first is right on Sultanahmet Square, the latter is in Tophane-Karaköy, not far from Istanbul Modern and Witt Istanbul Hotel.