Out of curiosity, what do you do in Shenzhen for 3 days? There are a lot of good restaurants there, but it's a brand new city, built almost entirely within the last 15 years. There's a lot of rather odd architecture but, for the most part, it's just tall office and apartment buildings (with some good shopping). The China cultural parks are nearby and, if someone will have no other opportunity to visit the PRC, can be fun, particularly Splendid China. Beyond that, though, I can't think of why Shenzhen would be a destination, other than to say, "I went to mainland China." Guangzhou would be a much more interesting choice, I would think. I have a warm spot in my heart for Shekou (I met my wife there), but there's little worth seeing for a tourist except, perhaps, the market streets.