Istanbul is a beautiful city with so much to see and do. Here's an ideal itinerary for 4 days in Istanbul:

Day 1:

Start your day by visiting the iconic Hagia Sophia, which was once a church, then a mosque, and now a museum. You'll be amazed by its stunning architecture and history. After that, head over to the Blue Mosque, which is just across the street from Hagia Sophia. This mosque is known for its beautiful blue tiles and six minarets.

For lunch, try some traditional Turkish food at one of the many restaurants in the Sultanahmet area. After lunch, visit the Topkapi Palace, which was once the residence of Ottoman sultans. You can explore the palace's many rooms and gardens, and even see the famous Topkapi Dagger.

In the evening, take a stroll through the Grand Bazaar, one of the largest and oldest covered markets in the world. You can find everything from spices to jewelry to textiles here. End your day with a dinner at one of the many restaurants in the area.

Day 2:

Start your day by visiting the Basilica Cistern, an underground water reservoir built in the 6th century. It's a unique experience to walk through the dimly lit cistern and see the columns and statues. After that, head over to the Spice Bazaar, where you can find all kinds of spices, teas, and sweets.

For lunch, try some delicious Turkish street food like simit (a sesame-covered bread) or döner kebab. In the afternoon, take a ferry ride along the Bosphorus Strait, which separates Europe and Asia. You'll get amazing views of the city and its many landmarks.

In the evening, head over to Taksim Square, which is known for its lively atmosphere and nightlife. You can find plenty of bars, restaurants, and clubs here.

Day 3:

Start your day by visiting the Dolmabahce Palace, which was built in the 19th century and served as the administrative center of the Ottoman Empire. You'll be amazed by its grandeur and opulence. After that, head over to the nearby Ortakoy neighborhood, which is known for its beautiful mosque and waterfront cafes.

For lunch, try some seafood at one of the many restaurants along the Bosphorus. In the afternoon, visit the Istanbul Modern Museum, which showcases contemporary Turkish art.

In the evening, take a walk through the trendy Karakoy neighborhood, which is known for its street art and hip cafes. You can also visit the Galata Tower, which offers amazing views of the city.

Day 4:

Start your day by visiting the Chora Church, which is known for its stunning Byzantine mosaics and frescoes. After that, head over to the nearby Fener and Balat neighborhoods, which are known for their colorful houses and historic churches.

For lunch, try some meze (Turkish tapas) at one of the many restaurants in the area. In the afternoon, visit the Istanbul Archaeological Museum, which has an impressive collection of artifacts from ancient civilizations.

In the evening, take a sunset cruise along the Bosphorus Strait. You'll get amazing views of the city's landmarks as the sun sets over the water. End your day with a dinner at one of the many seafood restaurants in the area.

I hope this itinerary helps you plan your trip to Istanbul!