The Trummelbach Falls are Europe's largest subterranean waterfalls.  They alone carry the melt water of the glaciers from the Jungfrau down to the valley, up to 20,000 litres of water per second.  The water carries with it over 20,000 tons of boulders and scree per year and causes the entire mountain to shudder and make a thundering noise.

                                                                     

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