China is building up a large collection of the biggest things in the world. The latest addition is the world's largest building. It is called the New Century Global Center and it opened this week in Chengdu, Sichuan province, in China's southwest. It is 500 meters long, 400 meters wide and 100 meters high. The area inside covers an amazing 1.76 million square meters. The building is so big that 20 Sydney Opera Houses could fit inside. It is almost three times the size of the Pentagon in Washington, D.C. It took thousands of workers just three years to build the enormous structure. The center is an important part of plans to make Chengdu a 21st-century city. It fits with the city's slogan, "Chengdu – Can Do".