Kupala Night – Kupala Night, (Ukrainian: Іван Купала; Belarusian: Купалле; Russian: Иван-Купала; Polish: Noc Kupały), is celebrated in Ukraine, Poland, Belarus and Russia, currently on the night of 6/7 July in the Gregorian calendar, which is 24/25 June in the Julian calendar. Calendar-wise, it is opposite to the winter holiday Koliada. The celebration relates to the summer solstice when nights are the shortest and includes a number of Slavic rituals.[1]

Kupala Night – Wikipedia

https://en.wikipedia.org/wiki/Kupala_Night

Kupala Night, (Ukrainian: Іван Купала; Belarusian: Купалле; Russian: Иван-Купала; Polish: Noc Kupały), is celebrated in Ukraine, Poland, Belarus and Russia, currently on the night of 6/7 July in the Gregorian calendar, which is 24/25 June in the Julian calendar. Calendar-wise, it is opposite to the winter holiday Koliada. The celebration relates to the summer solstice when nights are the shortest and includes a number of Slavic rituals.[1]