June 12 is Helsinki Day (Helsinki-päivä), a celebration of the founding of Helsinki. The first Helsinki Day was celebrated on June 12, 1959, the 409th anniversary of the founding of the city. The celebration includes many free events such as morning coffee, music, dance, films, food, sports, and tours.
I have not discovered any Finnish ancestors, but I visited Finland, including Helsinki, in 2008 and had a wonderful time. Helsinki is a beautiful city.