Kept at a slightly higher air pressure, this central service tunnel prevents smoke from entering during emergencies and acts as a safe evacuation route.

Over five million tons of excavated chalk were deposited into the sea near Dover to create Samphire Hoe, a 74-acre park that now hosts diverse wildlife.

Extracting the massive drilling equipment was deemed too costly, so British crews simply steered their machines downward and entombed them.

High-speed trains create a piston effect by compressing air ahead of them, so cross-ducts were added to vent this intense aerodynamic drag.