The snowy peaks of the Doldenhorn massif rise high above the railway base tunnel through the Lötschberg mountain. As rain and meltwater flow down through the calcareous mountain rocks, they are warmed as a result of compression. The clear water emerges at the northern end of the tunnel near Frutigen as a warm alpine stream with a temperature of around 18 degrees. Allowing the warm water to flow directly from the tunnel into a watercourse there would endanger native fish species. So what should we do with this heat? The idea was ingeniously simple – use the excess heat to grow warmth-loving plants and fish. This avoided the need to provide an expensive and energy-intensive cooling system for the tunnel water while at the same time enabling the thermal energy to be sustainably harnessed for a practical use. From this idea was born Tropenhaus Frutigen. The combination of tropical atmosphere, aquaculture and alpine environs is wholly unique in the world. Closed-loop material cycles and renewable energies are not merely theoretical concepts here, but can be seen and experienced directly.

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