This piece is over five years old, but well worth reposting:
Ever since Isaac Newton first described the laws of gravity in 1687, scientists have known that the quickest route between two points is along a straight line through the Earth's interior. Through the magic of gravity, any object dropped into such a "chord tunnel" at one end will emerge exactly 42 minutes later at the other end, no matter the distance. But for hundreds of years, the technical challenges of building such a tunnel were so daunting that it remained a theoretical curiosity. Only at the start of the 20th century did the idea become technically feasible, and to this day the tunnel linking the East Bay with New Jersey remains the only structure of its kind in the world.