Have I blogged about this before? If so, please forgive me. If not, enjoy the fun that Chronotrains brings you - a website where you can state a place of start and a time and then see how far you can get by train, in that time.
I can get, for instance, to the very south of Denmark in just under 8 hours. Or to Den Haag. It's quite fun to play around with, and sometimes very sobering how much possible distances depend on the network you have access to. (And for really long trips, I usually prefer a night train, even if that takes longer - because I never count the time that I'm sleeping as full travel time...