It's the midsummer Eve's eve. The day most of us Finn's head towards north to the cabins, camping areas or other places to spend the weekend. For the next three days our cities are mostly deserted. It's hard for me to even imagine the midsummer in the city.
Midsummer is the old celebration of the longest day of the year during the summer solstice. Of course the Christianity has assimilated it as many other old mark days and for most it's known as the day of the John the Baptist. In Finland the day is even called Juhannus after him.
The church holiday is aligned with the Christmas half a year apart. Except where Christmas day is on 25th the midsummer is on 24th. This is due the old Roman way of counting the days from the end of the month so June having 30 and December 31 explains the difference.
In Finland we don't have a fixed date for the midsummer. Instead we celebrate it on the Saturday of the week the of the summer solstice. So this year it will be on 26th. Of course, like with Christmas we are anxious for these celebrations and the eve in both cases is the more important day for us.