The Slavic summer solstice festival involving bonfire-jumping and magical herbs is Kupala Night.
Kupala Night, also called Kupala’s Night or simply Kupala, is a major folk holiday in several Slavic countries. It is linked to the summer solstice and, after Christianization, to the Nativity of Saint John the Baptist. Depending on the region and calendar, celebrations occur around June 21–24 or on the night of July 6–7 in areas following the Julian calendar.
Its rituals combine fire, water, plants, music, and courtship. Participants gather herbs and flowers, make wreaths, bathe or send garlands down rivers, dance and sing, and leap over bonfires. In some traditions, jumping successfully—especially while holding hands with a partner—was treated as a sign of happiness or future marriage. Folklore also claimed that supernatural forces were especially active that night, and that magical plants or fern flowers could reveal hidden treasures or grant special knowledge. Kupala Night should not be confused with Koliada, the winter solstice tradition.