That submarine is sadly at the bottom of the Atlantic now. They were hauling it to the US to appear in a film, the Harrison Ford movie K-19 I believe, when it sunk. There’s a Finnish submarine that was used during the war you can visit in Suomenlinna though. http://en.wikipedia.org/wiki/Finnish_submarine_Vesikko
They’re washing their carpets with pine soap as is the tradition. Watch an old Finnish film and there’s bound to be a scene where the lovely love interest, usually a maid, washes her employer’s carpets. I don’t think anyone actually wash their clothes in the ocean anymore.
You could also check if the timing works for a Baltic Cruise. The one I took several years ago did stop in Helsinki but also Tallin, St Petersburg, Stockholm and a few others, all of which were more interesting than Helsinki. If the timing worked to be in Helsinki at the same time as the festival, it might be a cheaper way of seeing a lot of places in a short period of time.
I did this just about a year ago - starting and ending in Copenhagen, and hitting all the places you mentioned, as well as Helsinki, and a port in northern German where most people took a tour of Berlin. We skipped that since we did it before and since our daughter who went with us now lives in Germany.
The plus side is that, as you say, you see a lot of places quickly. Even better is that, except for St. Petersburg, the ship docks very close to the center of these cities, and getting to them is very simple.
The minus side is that you don’t have a lot of time anywhere. We stayed in Copenhagen before we departed, but I would have liked more time in Stockholm.
Because this is the internet, and you just never know. And I wouldn’t be completely surprised to see a restaurant actually called Ravintola - it could be some sort of hipster ironic place.
My last visit to Helsinki was about 15 years ago, though I stayed at a friend’s apartment for a couple of weeks in '93. That’s when I did all of my major sightseeing. I still have photos of the weekend wash crowd.
