Noc Kupały is a festival called Midsummer Night in English. They have a tradition of sending 1000s of paper lanterns in the air. It makes for spectacular video.

Midsummer Night , also called night kupalnÄ… , kupalnockÄ… , Kupala , Sobótka or sobótkami – Slavic feast associated with the summer solstice the Sun , celebrated the shortest night of the year, which is usually (not including leap year) from 21 to 22 June (later eve of St. John – also commonly called St. John’s at night and then having many borrowings from earlier holidays – is celebrated with a 23 to June 24 ).
Feast of fire, water, sun and moon, harvest, fertility, joy and love, celebrated in areas inhabited by the Slav peoples, Baltic, Germanic and Celtic, and also by some people coming from peoples Finno-Ugric peoples , such as the Finns (in Finland, St. John’s night is one of the most important holidays on the calendar), and Estonians. (source)

via Colossal