Sana'a is one of these cities that is completely unique. It has been inhabited for over 2500 years, and all buildings in the walled old city were built before the 11th century. Most of these buildings have at least four floors and are ornately decorated.
The capital of Yemen is not just a marvelous open-air museum, though. It's also a bustling modern city. The old town is still very much inhabited, with shops, schools and mosques all in working order. Outside the city walls, traffic can be hellish.
For Western visitors, the exotic culture is another thing to marvel at. Women are dressed in black veils, only showing their eyes. Man can be seen sporting traditional daggers and chewing qat.