The LHC is currently the world’s largest and most powerful particle accelerator. It is the main accelerator at CERN, and consists of an underground tunnel 27-kilometres long (shown here in yellow) containing superconducting magnets, cooling systems and other infrastructure surrounding two beam pipes. These receive particles from a chain of lower-energy accelerators.
They are then forced to collide inside one of four gigantic underground detectors: ATLAS, CMS, ALICE and LHCb.
Main LHC website: http://home.web.cern.ch/topics/large-hadron-collider