Short answers, pulled from the story.
The Channel Tunnel is 50.46 kilometres long in total, with an underwater section of 37.9 kilometres, making it the longest undersea tunnel section in the world. It reaches a depth of 75 metres below sea level and runs on average 45 metres below the seabed.
The Channel Tunnel officially opened on the 6th of May 1994, at a ceremony in Calais attended by French president François Mitterrand and Queen Elizabeth II. Queen Elizabeth II travelled through the tunnel on a Eurostar train to reach Calais; both leaders then rode Le Shuttle to a second ceremony in Folkestone.
At 1985 prices, the Channel Tunnel cost £4.65 billion to build, representing an 80 percent overrun on the original £2.6 billion estimate. Financing costs alone ran 140 percent higher than forecast.
On the 1st of December 1990, Englishman Graham Fagg and Frenchman Philippe Cozette made the first crossing through the service tunnel, with the media watching. A BBC commentator described Fagg as the first man to cross the Channel by land for 8,000 years.
Ten workers were killed during construction of the Channel Tunnel between 1987 and 1993, eight of them British. Most deaths occurred in the first few months of boring.
Three main services operate through the Channel Tunnel: Eurostar high-speed passenger trains, LeShuttle vehicle shuttle trains for cars, coaches, and motorcycles, and through-running freight trains. In 2017, Eurostar carried 10.3 million passengers, LeShuttle moved 10.4 million passengers in 2.6 million cars, and freight trains transported 1.2 million tonnes of goods.