The document discusses Sky City, a supertall skyscraper in Changsha, China that was constructed in just 210 days using prefabrication techniques. The 220 floor building stands at 838 meters tall and cost $628 million to construct, making it the tallest building ever built in the shortest time. Prefabrication allowed Broad Sustainable Building Co., Ltd to construct the skyscraper much faster than traditional methods by assembling pre-made components off-site.