It's pitch black and a "fresh" eight degrees Celsius, summer or winter, but it doesn't stop visitors from flocking underground to learn about Switzerland's 'dark' past.
The La Presta asphalt mine in the western Travers valley was once the world's only source of the substance. Even though mining operations came to an end years ago, tourism has become the light at the end of the tunnel. An average of 21,000 people a year go underground at the site.
That is a considerable turnaround from the situation a few years ago when the mine's former owner, the Neuchatel Asphalt Company did not think it had a future as a tourist attraction.
But then a group of interested municipalities in the region and concerned private citizens came to the rescue and presto! La Presta was the place to visit in the Travers Valley.
Matthias von Wyss, who has been manager of the museum for the past 10 years, says it was simply a question of realising that you could not keep normal business hours when running an operation like this.
"You can't open at nine and close at five," said von Wyss. "It's important to make the site available at all times to the public."
The mine museum is open year round with guided group tours through the mine shafts.
A visit to the galleries takes in about one kilometre of the estimated 100 kilometres that were dug. The only equipment required is a hard hat, a strong flashlight, both provided by the museum, and a jacket or sweater against the constant eight-degree temperature and the 95 per cent humidity.
There are constant reminders that the miners were working in hostile territory. Water had to be pumped out regularly. There are areas showing how the walls were braced with wooden logs. In another section, Von Wyss points out massive limestone pillars that he said were literally supporting the farmland 25 metres above.
The history of asphalt mining in the Travers Valley goes back more than 250 years to 1711 when asphalt reserves were discovered by a Greek doctor, Eirini d'Eyrinys, who was interested in asphalt for medicinal purposes.
However, it took the business acumen of Philippe Suchard, the Swiss chocolate maker, to turn the mining operation from a sporadic business into a full-fledged industry.
Suchard promoted asphalt while also selling his chocolate around the middle of the 19th century. Thanks to him, the streets and sidewalks of London, Paris, Stockholm, Sydney and New York were literally paved with Swiss asphalt.
A visit to the mine today reveals why the asphalt was in such demand. The reason is simple, according to von Wyss. Up until the discovery of cheaper and better-quality deposits in Trinidad at the beginning of the 20th century, the mine at La Presta was the only major source.
Between 1890 and 1900 about 25,000 tons of asphalt were taken from La Presta a year. That rose to 53,000 tons by 1913. After that, war disrupted business, other suppliers came onto the scene and eventually mine operations ended in 1986.
With the opening of the museum, this dark chapter came to an end.
by Paul Sufrin