There are pictures of Knights fighting Snails in old Medieval manuscripts - and nobody knows why.
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A waterfall known as The Devil's Kettle empties water into a hole and nobody knows where it ends up!
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There's a mysterious dwarf planet between Mars and Jupiter called 'Ceres' which has never been visited by spacecraft or photographed in detail, however, Earth-bound telescopes reveal a large bright shining spot on the surface of this planet, the origin and nature of which are unknown.
5
There is a mysterious and loud radio signal known as 'the space roar' that has yet to be explained.
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