To build this dam, engineers first drowned a waterfall twice the size of Niagara. You could hear it roaring from 20 miles away. Then they made one of the world's biggest rivers move out of the way, just to clear room for the construction site. It's the Itaipu Dam, on the Paraná River where Brazil meets Paraguay. Work started in 1975, and the first job was the river itself. Crews spent three years carving a 1.2-mile channel through solid bedrock, 500 feet wide and 300 feet deep. They hauled away 50 million tons of earth. In October 1978, they set off 58 tons of dynamite, forcing the Paraná into a brand new path. Only then could the dam itself start to rise. The structure ate roughly five times the concrete used for the Hoover Dam, plus enough steel to rebuild the Eiffel Tower 380 times over. On one day in November 1978, the site poured concrete fast enough to put up a 10-story apartment building every hour for 24 hours straight. The main wall is 643 feet tall, the height of a 65-story tower. It runs almost 5 miles across the river. The bill came to $19.6 billion in 1970s money, roughly $60 billion today. About 40,000 people lost their homes when the reservoir filled. And in October 1982, when the water rose in just 14 days, it drowned Guaíra Falls, a chain of 18 waterfalls on the Brazil-Paraguay border that carried double the water of Niagara. Months earlier, a footbridge over the falls had collapsed under crowds of last-look tourists. Twenty-six died. In 2016, the dam produced as much electricity in a single year as New York City uses in two. That set a world record only broken in 2020 by China's Three Gorges Dam, which has 60% more generating power but sits on a river that runs low for half the year. Since 1984, Itaipu has put out more electricity than any single power plant in human history. It supplies around 90% of Paraguay's electricity and roughly 10% of Brazil's, from one wall of concrete. The final construction loan was paid off in February 2023, almost 50 years after the treaty was signed.