Location: CERN, Switzerland/France, Europe
Length: 16.6 miles.
Completed: 1988
Perhaps the most interesting tunnel on this list, the Large Electron-Positron collider tunnel is the only one on the list you'd have some trouble trying to travel through. Built in 1988, the tunnel at CERN's complex on the Franco-Swiss border has been the home to several particle accelerators used by nuclear researchers at the center.