There is an elaborate system of caves beneath the forest surrounding Winden, the extent of which most residents are completely unaware. Teenagers dare each other to visit the eerie caves, drugs are hidden there, and there's even a store of radioactive waste. Deep in one of the caves is a passage that can be used to travel through time.
Three heavy doors, each emblazoned with the Triquetra symbol and the text, "Sic Mundus Creatus Est," open to a man-made tunnel that houses the passage linking three points in time: 1953, 1986, and 2019. In November 2019, Mikkel Nielsen travels via this passage to 1986. Jonas Kahnwald, Ulrich Nielsen, and Helge Doppler likewise use the passage.
The yellow barrels
Countless yellow barrels filled with radioactive waste are stored in a cave beneath the nuclear power plant. They are the result of an accident cover-up from 1986. Plant director Claudia Tiedemann closes off access to the barrels with a heavy iron door. When investigations of the missing children threaten a search of the power plant site, Aleksander Tiedemann has the barrels removed from the cave and driven away in a truck.