For centuries, a narrow strip of water called the English Channel separated England from mainland Europe. The Channel is only about 21 miles wide at its narrowest point, but it was enough to keep Britain isolated as an island nation. On May 6, 1994, that barrier was broken. The Channel Tunnel, nicknamed the "Chunnel," opened for passenger service. It runs 31 miles under the sea between Folkestone, England, and Calais, France. Building the tunnel was an enormous engineering challenge. Workers dug from both sides at the same time, using massive drilling machines called tunnel boring machines. Each machine was as long as two football fields. They carved through chalk rock beneath the ocean floor. After three years of digging, the two tunnels met in the middle with almost perfect alignment. The Chunnel is actually three tunnels: two for trains and one for maintenance and emergencies. High-speed trains carry passengers from London to Paris in about two hours and fifteen minutes. The tunnel changed the geography of travel in Europe. England was no longer physically cut off from the continent. People, goods, and ideas could flow freely through the tunnel day and night.