In Europe you can hop on a train or bus or car and visit 10 countries in a day.
Europe's not quite that small. You could do it with a sports car or private plane I suppose, but your life would be truly miserable.
That'll actually be a nice challenge, I'll need to try that one of these days.
I'm in Luxembourg, so 2 countries is about 5 minutes, 3 about half hour, 4 about an hour. 5 about 3 hours, but then it's getting somwhat pesky.
Starting in Dover/UK, I can do France, Belgium, NL, Germany, Luxembourg, then down south to Switzerland, Italy, back to France, taking Monaco into Spain. Around 2000 km, that'll be 20 hours of driving.
Better way: starting in NL, doing B, then down to Lux, dashing over to Germany, Switzerland, taking Lichtenstein, Austria, then down to Italy, over to France and Monaco. 1500 km.
Good plan, I'll try that next summer :)