The Large Hadron Collider (LHC) is the world's biggest and most powerful particle accelerator. It was built by the European Organization for Nuclear Research (CERN). It is a giant circular tunnel built underground. The tunnel is 17 miles (27 kilometers) long, and between 50 and 175 meters below the ground. It lies beneath the border of Switzerland and France. 10,000 scientists and engineers from over 100 different countries worked together in the making of this project, and it cost 10.4 billion Swiss francs ($10 billion) to build. It is now the largest and most complicated experimental research facility in the world.