Today, we're going to build the highest bridge on planet Earth. Welcome to the Qinghai-Tibet Plateau, the “Roof of the World.”It’s home to the world’s tallest mountain, Mount Everest. But also the longest, deepest canyon on the planet, the Yarlung Zangbo Grand Canyon. This super canyon is 505 km (313 mi) long and 6 km (3.7 mi) deep. And it’s here that we’ll be taking on one of the most epic engineering challenges ever.