The Sonnenberg Tunnel is a long motorway tunnel, constructed between 1971 and 1976 and located in Lucerne, Switzerland. At its completion it was also the world's largest civilian nuclear fallout shelter, designed to protect 20,000 civilians in the eventuality of war or disaster. Catherine Frammery, "Dans les entrailles du Sonnenberg, monstrueux témoin de la Guerre froide", Le temps, Monday 15 August 2016 (page visited on 15 August 2015).
