I'm going on tour with my choir to Estonia, Latvia, and Finland in March/April. My wife and I have delayed our return airline tickets from Helsinki so that we can spend another 2 weeks in Europe. We will be finishing the choir tour in Helsinki. Anyone have any ideas? We are not sure whether its best to try to get to a bunch of countries or to explore a couple in detail. We are also not sure what format to utilize for our travels (Eurail, car, etc.) We are interested in exploring Norway and Sweden and maybe dipping into any or all of Poland, Russia and Denmark depending on the route we take and how much time we have.
The most obvious option (after seeing Helsinki, itself) is catching the overnight Silja Line ship to Stockholm. It's a 17-hour cruise & once you factor in the value of the lodging for the night, it's a good deal, fun and beautiful, too.
Stockholm is a beautiful city, worth 3-4 days at least. Oslo is a 6-hour train ride farther west and worth 2-3 days. Bergen, in the fjord country, is another 6-hour train ride west with many options for spending more time in the fjords. If you are into that sort of scenery, you could easily spend a week around there. So that would be an excellent two weeks.
Do you have to fly home from Helsinki?
If so, going so far west becomes problematic. In theory, you could go from Bergen to Copenhagen and then back to Helsinki by overnight ship. But that's a lot more moving around. You could also look into SAS airlines for economy fares from various Scandinavian cities.
It might be nice to spend late March in a warmer climate (I don't think Poland is much warmer than Scandinavia then) with more daylight. You might want to look into a cheap flight to Italy or Greece.
While in Helsinki, be sure to visit;
http://www.sacred-destinations.com/finland/helsinki-rock-church-temppeliaukio
And try to sing there, if possible. Something about it touches the soul in a way even gothic cathedrals cannot.
The other alternative would be to take the ferry across to Tallinn in Estonia (about 1 hr) and from there move to Vilnius, Lithuania and from there into Poland. Travel between Tallinn and Vilnius is easily done using Eurolines though it will be a long journey since you will already have seen Latvia and Estonia. I believe the last segment to Poland can be done on the train (which no longer goes through Belarus saving you the hassle of getting a visa).
A variation could also be taking the daily train directly to St. Petersburg and from there either going to Moscow and then backtracking or try and make your way to one of the Baltic nations.
Based on your post, I'm unclear whether your return home is from Helsinki or if you have the option to fly from another city. If Helsinki, you have a lot of backtracking to do no matter which direction you go.
For me, it would be a combination of ferries to Tallinn and/or Stockholm and the train tour to St. Petersberg from Helsinki (that someone mentioned on this site).