Earlier quoted context omitted.
It's not a long route, just 3.5 hours one way, but they are preparing to restart the "allegro" (St Petersburg - Helsinki) high-speed train service soon, iirc. The fun part is: Finland now requires a proof of vaccination to enter but doesn't recognize Russian vaccines, and vice versa. So as a Russian, if you really want, you could get Pfizer or something in countries that would let you enter with a PCR test or recogni…
They did restart it on last Sunday. Link in Finnish: https://yle.fi/uutiset/3-12222441 The link states that two daily Allegro services have been re-instantiated. Due to Russian legislation, using the service is only possible for Finnish and Russian citizens. It is true that EU and Russia do not recognise each other's vaccines, but a negative test result allows travel. Russia seems to require a test result in any case…
But then even if you are admitted into the EU, you would be considered non-vaccinated for any place that requires a proof of vaccination, and from what I heard there are many such places.