Washington, DC, is the capital of the US but also home to almost three quarters of a million people. The architecture is varied and increasingly high rise. Driving around DC, I realize how much I do not know about the architecture or history of DC. For a guide to the basic styles of homes in DC, check out this link.
In the fall, I decided to visit some of the former “iron curtain” countries and I decided to start at the top. Estonia is small but lovely.
Tallin is a wonderful old medieval town with modern technology and efficiency. The architecture in the old town was delightfully old and out of a fairytale.
Much of the town is Baroque and from the 17th century. I like the older bits better.
The Hagia Sophia (Aya Sofia) has survived so much history that it seems impossible for more stories to be added to her walls. But, she can support it all. One of my favorites, this is possibly the greatest building ever built. 
Come visit Istanbul and the Hagia Sophia!