Perhaps ask in those forums rather than the forum for a small island in the middle of the Atlantic Ocean!
Hahahah. Sorry about that
What an incredibly broad question. Obviously you cannot see much in 7 days, certainly not 3 COUNTRIES!
Pick two cities in one country and go from there. Depending on which two you decide on will determine whether you should fly into one and out of the other or into and out of the same one. With any luck you will pick two with good train service between them.
yes, try using or looking at a map of where you want to go.
You have COUNTRIES listed and they are not small places either.
one site you for to look at is...
alot of great train info.
note you will loose at the MINIMUM 1/2 day moving your base.
One last comment. I hope you know that you will loose 1 full day traveling to Europe.