Some 15 kilometres away from Vienna, there is a cave with an underground lake, which used to be a gypsum mine – the Seegrotte in Hinterbrühl.
During the Second World War it was used for the production of Nazi fighter jets, but it has now retired and is enjoying the sweet life of being a tourist attraction. If you go there, your tour guide will tell you stories of the cave’s olden days, when it was an active mine. People used blind horses to carry material then, because they were the only ones which wouldn’t get scared of going inside.
Thousands of litres of water have to be pumped out every day, so the cave doesn’t fill with water. Thanks to this, visitors can enjoy a sweet boat ride in the underground lake. If, during this ride, you can’t fight the feeling that Harry and Dumbledore were here looking for a horcrux, don’t worry – as far as I know, no magical zombies are allowed in there.