The Blue Mosque
Built 1609 - 1616
Called the Blue Mosque because of it's blue tile interior.
Still used as a mosque.
Topkapı Palace
Built between 1459 and 1465
Was the residence of the Ottoman Sultans for 400 years.
Now a museum, and it includes the beautiful Harem where
the Sultan's wives, concubines and children lived.
I haven't been to the Harem yet, but it's high on my list
for things to do during the less crowded season.
Hagia Sophia
The "church of holy wisdom" was inaugurated in 537 AD,
which means Hagia Sophia is close to 1,500 years old....
Converted to a mosque in the 15th century, and now a museum.
There is said to be rune "graffiti" from vikings visiting in the 9th century. When I walked in to Hagia Sophia for the first time, I was blown away, and I can't imagine what impact it must have made on a short viking who was used to much more modest architecture.
Basilika Cistern
Water reservoir from 532 AD
The Ottomans did not know of the cisterns existence until they discovered
that citizens caught fish by lovering buckets into holes in their basements.