THE Sydney Opera House, a UNESCO (联合国教科文组织) world heritage (遗产) site, turned 40 years old on Oct 20. Thousands of people celebrated with dances and even a huge cupcake. The opera house is one of Australia’s best-known landmarks. It holds 2,000 shows every year, bringing in 8.2 million visitors. It was designed by a Danish man, Jorn Utzon, in 1956. People planned to build it in four years, but it took them 14 years. Why? It has vaulted roofs (穹形屋顶) without any pillars (柱子) that made it difficult to build.