Beijing National Stadium
The eastern and western stands of Beijing National Stadium are higher than northern and southern stands.  This is in order to improve sightlines. A 24-hour per day rainwater collector is near the stadium. After water is purified, it is used throughout and around the stadium. Pipes were placed under the playing surface to gather heat in the winter to warm the stadium and coldness in the summer to cool the stadium. The stadium's design originally could fit 100,000 people. 9,000 seats were removed from the design. Then 11,000 temporary seats were removed after the 2008 Olympics.  Now the stadium can have 80,000 people.