It's a huge station, but the directions between va...

It's a huge station, but the directions between various interchanges are clearly marked. I have switched between the Underground/National Rail/Eurostar a few times, and never encountered any difficulties whatsoever. They have also put a piano in the Eurostar Concourse (which I must say is beautifully designed) and as I walked by a lady was playing it melodiously. To add to it, there are lots of shops where you could grab a bite, get a cuppa and indulge in some retail therapy (if that's your thing).