I've been to Istanbul several times when visiting Turkey, and never tire of the hustle and bustle of the city. Although a visitor could easily spend a week or more in the city, it's possible to see most of the iconic sites of the city in just one day since they are all located near each other in the Sultanahmet neighborhood, which sits right on top of the old Byzantine city. These must-see sites include:
The Hippodrome is one of the oldest sites in Istanbul, dating back to the second century AD. This large arena was used for chariot racing and other events and was the center of the city for over 400 years. None of the original Hippodrome remains, but the site is now a park that includes three ancient columns including an obelisk brought to the city from Egypt in 390 AD.
The Blue Mosque looms over the Bosphorus, and its six minarets make it easy to spot. The Blue Mosque is still an operating mosque, but visitors are allowed inside to see the magnificent blue tiles from which the mosque takes its nickname.
The Basilica Cistern is the largest surviving Byzantine cistern in Istanbul. Since it is underground, it is cool in the summer. I loved the 336 huge columns and was impressed that water was pumped from the cistern throughout the city using 40 miles of aqueducts.
The Hagia Sophia was the world's greatest Christian church until the Ottoman conquest in the 15th century. The Ottomans transformed this magnificent building into a mosque, but today it is a museum. Restorers continue to work on the building, so each time I've been I've seen something new.
The Topkapi Palace is the ancient home of the Ottoman sultans, but has been a museum since Turkey became a Republic in the 1920's. The grounds, structures (like the harem), artifacts, and jewelry make this a must-see site.
The five sites listed above are all within easy walking distance of each other. Two other sites are nearby, but you probably want to take a taxi or public transportation. I'd be remiss if I didn't mention the Grand Bazaar and the Spice Market. Dedicated shoppers could spend days in either of these. The Grand Bazaar is much larger, and one can easily get lost. The Spice Market features a memorable mixture of smells, sounds, and sights and is a photographer's dream.
Although Istanbul is a great cruise port of call, Louis Cruises has partnered with Turkish tour operator Karavan Travel to offer travelers the option of taking a cruise of the eastern Mediterranean in combination with a land tour of Turkey. These cruise and land tours include a four- or five-day cruise of Turkey and some of the Greek Isles on the Louis Cristal, along with a multi-day land extension to other parts of Turkey. A cruise tour like this one can provide a travelers the opportunity to get a taste of much of this exciting part of the world efficiently, while letting someone else do the driving.
I participated in one of the Louis Cruises/Karavan Travel cruise and land tours in western Turkey that included visits to Istanbul, Izmir, Pergamon, Pamukkale, and Kusadasi. We enjoyed a hotel stay at the Hilton Garden Inn Golden Horn in Istanbul before flying to Izmir and an overnight stay at the Point Hotel Taksim at the end of our cruise tour. Both hotels were very good, although we didn't spend much time there (other than to sleep).