Inside the Hidden Escape Tunnel for the World's Longest Under-Sea Tube

We love huge tunnels here at Gizmodo, whether we're watching them being built or pondering the mysteries they unearth. So when The Telegraph got the chance to explore the service tunnel that supports The Channel Tunnel, our ears perked right up. Check it out—it's astoundingly huge.

The service tunnel runs in between the two main tubes that convey trains from Folkestone, England to Coquelles, France, and vice-versa. At the midpoint halfway along the 31 mile tunnel, passengers are sitting nearly 330 feet below the English Channel.

The Chunnel boasts the longest undersea portion of any tunnel in the world, so a dedicated evacuation route is a necessity. A series of doorways connect the service tunnel to the England-bound and France-bound tubes, so that in an emergency, passengers can evacuate from a disabled train into an open tube with fresh air and space.

The Chunnel really is monumental—first proposed in 1802, construction started and stopped a bunch of times before the project was finally completed in 1994. Not many people have seen the inside of the service tunnel. Here's hoping you'll never have to see it firsthand. [The Telegraph]