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Founded in 1954, the European Organization for Nuclear Research (CERN), 8km west of Geneva, is a laboratory for research into particle physics. It accelerates protons down a 27km circular tube (the Large Hadron Collider, the world's biggest machine) and the resulting collisions create new matter. Come anytime to see the permanent exhibitions shedding light on its work, but for two-hour guided tours in English reserve online up to 15 days ahead and bring photo ID.
Tours often fill up months ahead – access the online booking portal at http://visit.cern/tours/guided-tours-individuals. To get here take tram 18 from the main train station.