Xi'an was China's capital for eleven dynasties and the eastern terminus of the Silk Road. Today it's a city of 8 million, mostly unremarkable in appearance, but it holds some of the most significant historical sites in Asia. The Terracotta Warriors alone justify the trip.
The city centre is enclosed by remarkably intact Ming Dynasty walls. Inside them, the Bell Tower marks the intersection of the main axes. The Muslim Quarter to the northwest — a dense grid of alleyways around the Great Mosque — has been home to a Hui Muslim community for over a thousand years and has an entirely different character from the rest of the city. Come here to eat: lamb skewers, roujiamo (meat in flatbread), and liangpi (cold noodles) are the staples.
The Terracotta Warriors are 40km east of the city, easily reached by bus or taxi. Give them a full morning. The city walls can be cycled in about two hours. The Shaanxi History Museum, inside the walls, has one of China's finest collections of Tang Dynasty artefacts. From Xi'an you can travel the Silk Road west to Turpan and Kashgar.