Olympic Green
It is the main area of the celebration of the 2008 Beijing Olympic Games and is now one of the most emblematic places of the city. It is located to the north, and is easily accessible by metro. I recommend going at sunset to see it lit, but beware that you aren´t too late because I think at 21 or 22 they close the premises. Here you can see great works of modern architectures such as the Water Cube Beijing Olympic Stadium, better known as the nest.