The alpine expedition began for swissinfo where the Muotathal valley ends. But instead of ascending peaks, it descended deep below the base of the mountains.
At 190 kilometres in length, the Hölloch - or Hell’s Hole - cave system is the longest in Europe.
Guide Thomas Frauenfelder refuses to go along with the joke that he is opening the gates of hell as he unlocks the door to the cave.
Even though “Hölloch” translates into English as Hell’s Hole, Frauenfelder says the first syllable of the word really means “slippery” in the local German dialect.
The vast underground network is a lot cooler than Hell must be, at a constant six degrees Celsius. Better yet, there is an escape route.
Guides are needed to get in and out since the Hölloch is a three-dimensional maze of narrow limestone tunnels, chasms, potholes and wide halls.
Winter is the season for caving expeditions, usually beginning in November and lasting until the end of March.
This is when the vast Hölloch network is dry since any precipitation falls as snow, which freezes, and no water seeps into the porous limestone.
When the snow melts in spring and is combined with rainfall, the Hölloch is transformed into a watery hell.
“The water gushes out everywhere when the system is full,” says Frauenfelder. “It exits the cave at 12,000 litres a second.”
The cave system was discovered in the late 19th century by a local farmer. In the early 20th century, a Swiss-Belgian group of investors pumped SFr1 million ($760,000) into the cave to turn it into a tourist attraction.
They used dynamite to extend the entrance, widened the main tunnel and installed electric lights, a luxury not even the villagers of the valley had at the time.
However, the seasonal flooding put an end to the electric lights and other installations, forcing the company into bankruptcy in 1917.
Since then, cavers have been able to explore the system in its more natural state.
It is estimated that the cave’s 190 kilometres is only one-tenth of its true length.
New recesses are continually being discovered and the system is expanding by about 370 cubic metres a year through erosion.
Three sub-systems make up the Hölloch cave, spread over a 22 square kilometre area and a depth of 650 metres.
The upper level is the oldest, predating the Pleistocene ice age, which is believed to have begun 1.8 million years ago.
Anyone wishing to explore the subterranean network can sign up for a simple stroll through the larger tunnels, or for a more adventurous trek into its narrower recesses.
The tours last a few hours to a few days, and those staying the night dine and sleep in subterranean caverns illuminated by candlelight.
Down to earth
Frauenfelder is a full time commercial pilot, but when he comes down to earth on his days off, usually heads underground.
He is passionate about caving and acts as a guide for the local adventure sports company, Trekking, which has a monopoly on cave tours.
“I need to come here to find a balance,” he reflects. “Once you are in the cave, time is no longer important.
“Basic human instincts are all that count,” he continues. “A group of people coming in here become much closer. If someone is afraid, he is offered a hand. You suddenly realise what is important in life.”
swissinfo, Dale Bechtel in Muotathal
A cave can only form if the following criteria are met:
The presence of porous rock (calcite, limestone, gypsum, salt)
A minimum number of cracks and crevasses
A difference in altitude between the place where the water enters and exits.
swissinfo joined a guided tour of the Hölloch cave system, in Muotathal, which was discovered in 1875 and is the longest in Europe.
According to estimates, Hölloch is expanding at a rate of 370 cubic metres per year.
There are 12 caves open to the public in Switzerland.