On May 6, 1994, Queen Elizabeth II and French president François Mitterrand held a ceremony opening the English Channel tunnel, or "Chunnel." Elizabeth rode a train through the Chunnel heading to France, while Mitterrand took a train starting in Gard du Nord heading toward England. Their trains pulled up and met on the same track, nose-to-nose, on the French side of the channel at Calais. Engineers took great pains ensuring the trains did not collide.

The Chunnel is a 23-mile undersea rail tunnel connecting England and France beneath the English Channel. Its opening marked the first time since the last Ice Age that the two land masses were connected. The Chunnel's rail service drastically simplified travel in both directions, removing the need for air or sea travel to hop over the channel. The rail service also allows passengers to load up their cars, so they can continue a road trip on either side.

The idea of bridging the English Channel had been kicking around since Napoleon's day, when French engineer Albert Mathieu-Favier dreamed up the idea of building a tunnel to convey carriages. The first attempt at building such a thing came in 1880, when about a mile of tunnel was bored before the project was abandoned. The Chunnel project itself formally began in 1987 on the English side (French side digging started in 1988), and cost $16 billion—about twice the original estimated price tag.

By 1999, the Chunnel turned its first profit. It took until 2007 to pay dividends to its investors—about a decade behind schedule. Today, it moves more than 20 million passengers and 19 million tons of cargo every year. It is the busiest rail line in the world.

Here's a video showing the opening, and a bit of history on the project:

For more Chunnel goodness, check out 10 Fascinating Facts About the Chunnel.