To celebrate the 30th anniversary of the Channel Tunnel, Practical Engineering takes a look back at the construction and operation of this incredible piece of infrastructure. This 30-mile-long underwater tunnel began construction in the 1980s, using giant Tunnel Boring Machines to drill out three tunnels, starting from either side and, incredibly, meeting in the middle. All that construction underground (and underwater) is no simple feat, as Grady discusses. He also takes a look at some of the operational challenges of the design, including managing heat and air pressure build-up. (Image and video credit: Practical Engineering)