Heineken Open'er Festival The Heineken Open'er Festival is the largest Polish open-air music and performing arts festival and definitely the most important music event in Gdynia - a city in the north of Poland at the Baltic Sea coast. The Heineken Open'er Festival is the largest Polish open-air music and performing arts festival and definitely the most important music event in Gdynia - a city in the north of Poland at the Baltic Sea coast. It is a special place on the Polish map, where people from more than 30 countries are meeting, enjoying the best performances and having the best weekend in the year. Total area of the festival in Babie Doly airfield makes 75 hectares of space for one to explore and contains 7 stages, around 120 artists, festival town with merchandising area, gastronomic zones, camp site, beach, sea and sun, space for sports activities and multimedia, NGO, films, theaters and performances. 10 hectares are dedicated to campers- place where the true festival admirers are sleeping in their tents after the sun goes up.