Kupala is a fertility festival with its roots in pre-Christian times. It celebrates, Kupala, the Slavic goddess of fertility and love. Any Kupala Night / Noc Kupały event in Poland generally includes wreath-floating of wreaths (wianki) and bonfire jumping rituals. Fire and water both being related to purification. Kupala takes place in villages and towns all across Poland around Midsummer on the night of 23rd/24th June each year.
Related content on Polish Poland: Wianki.