A fine rain was trickling along the gutters as we started our descent into the network of tunnels under the old town of Bern.This content was published on July 4, 2003 - 08:00
A three-metre flight of steps led down from the embankment of the River Aare into the bowels of the earth.
Beneath the clean streets, used water, human waste and other detritus are whisked away, out of sight, through 320 kilometres of tunnels spanning the length and breadth of the medieval city.
Our guide was Markus Neuenschwander, former professional diver turned pumping plant manager.
He explains that this old part of the sewer, dating back to the Middle Ages, provided an escape route for members of the city government in the event of attack.
The channels are directly below the government building, the Rathaus, and have stone steps and metal grips to provide a safe descent.
The sewers butt up to the city walls, and as we descend through the tunnels our guide points out the circular openings from which guards or fleeing governors may have shot at their enemy below.
Graffiti from the 19th century adorns the walls of an elegant spiral staircase leading down into a narrow passage below.
The original open gutters snaked between rows of houses, and sewage was flushed along by river water. A "Stream Master" was in charge of making sure the channels were scrubbed clean.
As the city grew, sanitary conditions deteriorated; the streets began to stink, and the Aare became a conduit for disease.
In 1866 and 1873, there were two typhoid epidemics. This led to the building of a comprehensive closed sewage network, with its own high-pressure water pump.
A law was passed in 1875 requiring all houses in the city to be connected to the new system.
The network now encompasses pumping stations, rain collectors, measuring stations to gauge the water level and extent of rainfall, and devices to relieve the pressure on the sewers when there is too much rain.
The pumping stations send most of the waste water from Bern and surrounding areas to the purification centre in Bern-Neubrück, opened in 1967.
Some 600 to 900 cubic litres enter the plant every second.
In 1315, it was one man's job to look after the sewers and keep them clean. These days, 13 sewage workers are employed to check the condition of the tunnel walls and to keep the system running efficiently.
Remote-controlled cameras are used to inspect 30km of smaller tunnels, some just 30cm wide.
Not a dustbin
Building engineer Thierry Kreienbühl says many items flushed down toilets cause blockages in the pipes.
There is evidence of this in the old sewage system, where discarded spoons, watches and children's plastic toys have been put on display to remind the visitor of what doesn't belong down the toilet.
Kreienbühl says nylon pantyhose are the worst offenders, as these become entangled in pumps.
Another problem is that people flush away food, which attracts disease-carrying rats - the cause of the plague in the Middle Ages.
Kreienbühl told swissinfo: "There aren't many here now, but if we do find them, we sometimes shoot them."
Our guide whisks us past highly sophisticated electronic control systems for pumps and water outlets, which whir into action with a show of colourful lights.
We watch the dramatic emptying of a water collector, creating a terrifying tidal wave of waste water.
We scamper like goats through narrow passages, and, fireman-like, scale steel ladders stretching up to the open sky. Then, to our complete surprise, we come across an underground beauty spot.
Beneath the Rose Gardens, which preside over a hill facing the medieval city, is a secret grotto. The cave is part of the underground excavations that form the modern sewers.
Water seeping through the rocks into this grotto has such a high calcium content, that the white deposit has solidified to form an arc of stalactites over a crystal-clear pool.
It is a treasure reserved for a few visitors and a host of sewage workers - a small but priceless reward for taking care of the human waste that we would all rather forget about.
swissinfo, Julie Hunt
Bern's sewers date back to the 14th century.
For many years, wastewater ran through open gutters between houses.
As the city expanded, disease spread.
In 1875, all homeowners were forced to connect up to a new, closed sewage system.
The network encompasses 320km of tunnels.
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