I was just going to suggest seat61! Awesome site, I've used it in the past to get ideas for my own rail journeys and it's especially good for learning about the longer ones. You can theoretically go all the way to Southeast Asia from Helsinki, using nothing but trains, and then connect by ship to Japan or Australia.

There was also a link on his site to a British railfan's blog about his trip to North Korea - he had all the documents he was supposed to have, but wasn't supposed to have been issued them (no foreign tourists through that entrance, or that part of NK), so his trip report is presumably one of a kind. Very interesting stuff.