The easiest way to get from Germany to Helsinki is by ferry, From Travemünde in Northern Germany it  just takes 31 hours. 

My slightly longer, but way more exciting trip to Helsinki led me on my honeymoon from our then home in New York City by car across the US and British Columbia to Vancouver, from there to Beijing where we hopped into the Transmongolian Railway to Ulan Bator and further to Lake Baikal in Siberia. From Siberia we boarded the Transiberian Railway across the Urals to Moscow. St. Petersburg was the next stop before we finally arrived in Helsinki. Unfortunately we just had one day and one night in Helsinki before we had to board the ferry to arrive in time for our wedding which took place in Germany in the course of this honeymoon trip.  Before leaving we ate the yummy Lohikeito soup refined with local salmon and potatoes. Instead of sightseeing we had to practice our Wedding Waltz in the streets. Condé Nast Traveller, my favorite travelmagazine if I want to indulge, voted Helsinki again as the most liveable city in the world. I need to come back.