When my wife and I went to London in our twenties (right before the girls were born) we traveled all over the country side. We stayed mainly in London, and we used the trains for our travelling.
We used the St. Pancras railway station a lot. It's a central London railway station that travels to several places. We used it to go to Brussels. We also took it to Paris and Nottingham. We loved every place we traveled to. Gosh, to be young again! I'd travel across Europe even more! I'm lucky I get to travel with my job.
However, it's mainly just in the states. While that's lovely and I'm not complaining, I would love to get to Europe again now that the kids are in college.
We would absolutely use the St. Pancras railway station again. The place is entirely majestic in it's nature. It looks like a castle from the outside-- it's so beautiful.