A geographic and metaphoric melding of East and West, Istanbul is the world's only city covering two continents -- the Bosporus Strait runs through the center, with Europe lying to the west, Asia to the east.
For nearly 2,000 years, the ideally situated metropolis has been the keystone of some of the world's great empires, serving as the capital city for the Romans (under the name Constantinople, as noted by the informative "They Might Be Giants" tune), Byzantines and Ottomans.
Inside the sprawling city, the secular and the sacred mingle: minarets and nightclubs, dusty prayer rugs and designer digs. The idea of Istanbul as collision between East and West reveals itself immediately, with monumental churches cum mosques (the Hagia Sophia), Roman ruins (the Hippodrome, where horse and chariot races were held in Roman times) and unadulterated symbols of consumerism (the Grand Bazaar with its thousands of shops).
Exploring Istanbul fully would take years, but you can see the highlights in about three days.
A note for Western travelers: In deference to Istanbul's beautiful mosques, churches and synagogues, it's advisable to wear respectful attire (long pants or long skirts) if you want to enter these historic sites. Women may be required to wear a head covering -- you can usually buy cheap scarves from vendors outside.
--written by Carolyn Spencer Brown, with contributions from Sarah Schlichter and Dan Askin