Kupala day is a pagan holiday still celebrated in some Slavic countries such as Russia, Ukraine, Belarus, and to some extent, Poland, and also included other segments of Europe and even India. That day is celebrated on the 7th of July though celebration starts a night before.
In particular, Bulgarians believed that on Kupala the Sun is "dancing" and "twirling the sabres". Polish girls baked ceremonial "sun" cakes while Englishmen sought out the fern, not for the sake of the blossom of a burning flower, but for its seeds which can make a man invisible.
On the eve unmarried young men and women gathered outside the village in the forest or near a stream or pond. There they built "Kupalo fires" around which they performed ritual dances (khorovod) and sang ritual folk songs.