There are several ways to come to Helsinki. Here are some hints how to come.
Directly by ferry from Travemunde to Helsinki ferry_travemünde_helsinki .
By car you have also several route possibilities e.g. you can drive to Tallinn and take a ferry from Tallinn to Helsinki or you can drive through Sweden either to Stockholm and take a ferry from there directly to Helsinki or to Kapellskär and take a ferry to Naantali.
Finnlines (ferry company) gives a certain discount on both routes (Travemunde-Helsinki and Kappelskär-Naantali), when you mention a code when ordering the transportation tickets. Ask more from your country’s IHA–President.