We went to the city to play in a park that is bigger than the ones near my host. The park personnel had organized a small festival. We got to put flowers on a "pole" (this has something to do with the swedish speaking Finns, they call it a "maypole"). There were different games to play - oh, and the fire trucks came and an ambulance and we got to see inside them! Then there was a chance to barbecue and all sorts of food! It was really fun 
Wikipedia says this about the Finnish Midsummer:
Before 1316, the summer solstice was called Ukon juhla, after the Finnish god Ukko. In Karelian tradition, many bonfires were burned side by side, the biggest of which was called Ukko-kokko (the "bonfire of Ukko"). After the celebrations were Christianized, the holiday is known as juhannus after John the Baptist (Finnish: Johannes Kastaja).
Since 1955, the holiday is always on a Saturday (between June 20 and June 26). Earlier it was always on June 24. A lot of the celebration of midsummer takes place on midsummer eve, when many workplaces are closed and shops have to close their doors at noon.
In the Finnish midsummer celebration, bonfires (Finnish kokko) are very common and are burnt at lakesides and by the sea. Often two young birch trees (koivu) are placed on either side of the front door to welcome visitors. Swedish-speaking Finns often celebrate by erecting a midsummer or maypole (Swedish midsommarstång, majstång).
In folk magic, midsummer was a very potent night and the time for many small rituals, mostly for young maidens seeking suitors and fertility. Will o wisps were believed to be seen at midsummer night, particularly to finders of the mythical "fern in bloom" and possessors of the "fern seed", marking a treasure. An important feature of the midsummer in Finland is the white night and the midnight sun. Because of Finland's location spanning around the Arctic Circle the nights near the midsummer day are short or non-existent. This gives a great contrast to the darkness of the winter time.
Many Finns leave the cities for Midsummer and spend their holiday in the countryside. Rituals include bonfires, sauna and spending time together. Heavy drinking is also associated with the Finnish midsummer.
Many music festivals of all sizes are organized on the Midsummer weekend. It's also common to start summer holidays on Midsummer day. For many families the Midsummer is the time when they move to the countryside to their summer cottage by the lake. Midsummerday is also the Day of the Finnish Flag. The flag is hoisted at 6 pm on Midsummer eve and flown all night till 9 pm the following evening.
