Shanghai is a very beautiful city -- I just love it. Take a river boat and go to Shanghai Tower.
Xi'an is ok and has great Chinese ambiance within the city walls, but I would not stay here more than two or three days. If you don't care about seeing the Terracotta Army and the Great Mosque, then don't bother to come here. The air quality is very bad here and there's not much to do here other than those two things.
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Shanghai is like any big city and it feels too Western. The old city and Yuyuan Gardens is touristy but beautiful and the area across the water from the Bund is beautiful. There is not much to do here, so after three days I was ready to move on.
Hangzhou is an absolutely beautiful city. I took it as a 4 day trip out of Shanghai where I was studying and fell in love.
I was recently down in Xi'an for a week and had a great time.
The Terracotta Army and the walled city are fantastic, inside the walls are old markets which are fun, but two days max is enough for Xi'an. Outside the walls are dreary houses and factories. Other downers are the taxi drivers who refuse to use meters, just get out of the cab, the beggars which to a Westerner are very aggressive, and the pollution is horrific, took two weeks to clear!! And the use of lights after dark on vehicles/cycles is a rarity so beware when walking, but otherwise it's very safe.
Wudang Shan (Wudang Mountain), the famous Taoist mountain, is close to Wuhan. Xiang Fan is a cool stopover to get to the mountain, about an hour away.
The old town is a must place to see. Go to Shangri-La.
I love Beijing! The air quality is terrible, the traffic is a nightmare, and all of the tourist sights are crowded, but I still love Beijing because there is so much to see and do. Locals are very friendly, but make sure you bring a Mandarin phrase book. I easily spent six days here.
Despite some negative comments given, Xi'an is a "real" Chinese city. The tourist sights are well known but it's a great city to get out and explore. Especially if you like inexpensive street food.
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