Topkapi Palace which is located behind the Blue Mosque and Hagia Sophia should be at the top of your places to see list in Istanbul! It embodies the ultimate Ottoman architecture, treasures, culture and relics, it has very beautiful gardens and is located at the entrance of the Bosphorus, hence amazing views of both the Bosphorus and the Marmara Sea.
During 400 years, it was the center of state administration and residence of Ottoman sultans. At the order of Fatih Sultan Mehmet, construction began in 1460 and finished in 1478. Until the 1850s, it served as a home to Ottoman sultans. In the beginning of the 19th century, the palace became inadequate for sultans. While Ottoman sultans moved to Dolmabahce Palace located on the Bosphorus, Topkapi Palace never lost its importance. The royal treasure, the Holy Relics of the Prophet Muhammad, and the imperial archives continued to be preserved at the palace. Ataturk ordered its transformation into a museum displaying the history and wealth of the Ottoman Empire. Compared to its size in the beginning, it is quite smaller, but still it is a huge building and there is a lot to see, so you need at least half a day to explore it.
You enter Topkapi Palace through the Imperial Gate. Before you enter the Imperial Gate (Bab-i Humayun), you can see the Fountain of Sultan Ahmet III built in 1728 by the sultan who was very fond of tulips. It perfectly reflects the architecture in the 'Tulip Period' of the Ottoman Empire. (Tulip period is akin to France Louis XVI and Marie Antoinette's "let them eat cake" period. It is when the sultans and his royal entourage were busy growing tulips while the empire was crumbling.)
After the Imperial Gate, you enter the First Court, known as the Court of the Janissaries. On your left is St. Irene (Hagia Irene) also known as the Church of the Divine Peace. At first it was a pagan temple and then was converted into a church. Now it is an amazing concert hall, possibly one of the most interesting locations for a classical music concert.
The Middle Gate (Ortakapi or Bab-us Selam) led to the palace's Second Court, used for administration of government. Only the sultan and the queen mother were allowed to enter the Middle Gate.
The Second Court looks like a park. It includes the great Palace Kitchens where an exhibition of Chinese celadon porcelain is located. These porcelains are famous for their color change. If poisoned food was put in them, they changed color, because poisoning-related deaths of sultans were very common in the Ottoman Empire. This court also includes the Inner Treasury, which exhibits Ottoman and European armor.
The Third Court, Gate of Felicity, was the entrance into a private place belonging to the sultans. The Imperial Treasury is located in this court, which displays an amazing collection of objects decorated with expensive and rare materials.
The Fourth Court exhibits the Topkapi Dagger where the Kaşıkçı (Spoonmaker's) Diamond, a teardrop-shaped 86-carat rock surrounded by 49 small diamonds, is displayed. It is the fifth largest diamond in the world.
You can also remember Topkapi Palace from wonderful films such as Jules Dassin's film "Topkapi." Mozart's "The Abduction from the Seraglio" centered on Topkapi Palace.
Since both the building and the relics are well preserved, you will feel like you are living in the Ottoman era.
Admission: Main palace ticket approx 950 TL (about $20). Harem section requires a separate ticket (approx 300 TL / $7).
Hours: Open daily 9:00 AM to 6:00 PM (summer), 9:00 AM to 4:45 PM (winter). Closed on Tuesdays.
Guided tours: Scheduled guided tours available at the main ticket office. Audio guides available in multiple languages (approx 150 TL / $3-4).
Time needed: Minimum 3-4 hours. The Harem alone takes 45-60 minutes.