Time Out says
Formerly the world’s largest civilian bunker, Sonnenberg tunnel is located in the heart of the city of Lucerne
This giant bunker was built between 1970 and 1976 at a cost of 40 million Swiss francs. If it ever had been needed, two motorway tunnels would have been sealed by four 350-ton gates, with room enough for 20,000 beds and hundreds of toilet cabins - in fact one third of the population of Lucerne would have found shelter here inside Mount Sonnenberg. In addition to the two tunnels, the bunker was equipped with a seven-floor, subterranean building furnished with a control office, a radio studio, an emergency hospital, detention cells and more.
The tour provides a fascinating insight into Cold War times and the fear of the nuclear bomb and illustrates the uses of the bunker today.