Poland
Especially in northern Poland - the Eastern Pomeranian and Kashubian regions (but also in all country), midsummer is celebrated on June 23. People dress like dangerous sea pirates, and girls throw wreaths made of flowers to the Baltic Sea, and to the lakes or rivers. The midsummer day celebration starts at about 8:00 p.m. and lasts all night until sunrise. People celebrate this special day every year and call it Noc Świętojańska what means St. John's Night. In that day in big Polish cities (like Warsaw and Kraków) there are organized many entertainments, but the most popular entertainment is Wianki what means wreaths.
http://en.wikipedia.org/wiki/Midsummer