To have the sun above the horizon at midnight you need to be inside the arctic circle. About half of Finland is. In Turku you are about 60 degrees north about 4 degrees north of Edinburgh so it stays light later for local solar time but not all night although at midsummer it will probably be twilight all night. The Arctic circle is at 66 degrees 33 minutes north. you need to travel about 400 miles north to get to a point where the sun stays above the horizon all night.