The Large Hadron Collider (LHC) is the world's largest and most powerful particle accelerator, located in a 27-kilometer circular tunnel deep beneath the border of Switzerland and France. While not a traditional 'monument,' it is one of the most significant engineering landmarks of the 21st century. It consists of thousands of superconducting magnets that must be cooled to -271.3°C—colder than outer space—using liquid helium. Inside the tunnel, two high-energy particle beams travel at close to the speed of light before being made to collide. This landmark allows scientists to recreate conditions that existed just after the Big Bang, leading to the 2012 discovery of the Higgs boson, the particle that gives mass to other particles.