Depending on the direction you're heading, Xi'an is either the start or the end of the Silk Road. In either case, it is one of the oldest and most important cities along the route. At more than 3,000 years old, Xi'an is an ancient city and for more than 1,000 years it served as the capitals of the Zhou, Qin, Han, and Tang dynasties.
Xi'an is a huge city of more than 6.5 million people living directly within the city limits, and 8.5 million total in the municipal area. There are a ton of historical sites in Xi'an, and many different nightlife options as you'd expect in a city as big as Xi'an. For information on getting around, what to do, and what to see, check out my guide to Xi'an.