By Jonny Dymond
BBC Europe correspondent
It's difficult not to feel a sense of relief as your train pulls out of Brussels. The headquarters of the EU is full of perfectly decent, very hard working officials, diplomats, lobbyists and journalists.
But they do have a rather bad habit of talking to themselves about subjects only they appear to care about in a language only they understand.
Brussels' officials, diplomats and lobbyists inhabit their own world
So watching the corporate headquarters that encircle Brussels flit past the window, and entering the flat lands of Belgium proper, your spirits tend to rise.
In almost no time the train is in Germany, the border marked not by police and customs officials but by the trilling of mobile phones receiving messages from their new service providers.
The train is full. In the middle of the carriage chatting away about every subject under the sun is a happily international group: Monica, from the Netherlands, Julia from Britain and Dorothea, from Germany - three middle-aged women on their way for a lunch date in Frankfurt.
Monica was full of praise for the achievements of the past - the euro, borderless Europe and the single market - but much more hesitant when it came to what the future held.
No-one in the group has anything to say about the subject which rivets Brussels - the constitution, or lack of it
"We're so different and so proud to be different and we have to keep on being different," she says, responding it seems to no particular threat to that "difference" but a more general unease about the direction of Europe.
No-one in the group has anything to say about the subject which rivets Brussels - the constitution, or lack of it. "No, no, no, not at all," says Dorothea, asked if she had thought about it.
"I haven't really thought about it all, no, to be honest," says Julia with a slightly embarrassed laugh.
But on the question of further enlargement of Europe there is unanimity. "It's the European Union," says Dorothea, "so every land of Europe should have the possibility. But just Europe, nothing else."
Drawing into Berlin's Hauptbahnhof, the new central station, it's difficult not to be impressed; this glass and steel cathedral of rail is also the new crossroads of Europe.
Berlin's station is brand new, but links to the East are still slow
Trains rumble in from Amsterdam and Brussels and trundle out to Moscow, Warsaw and Kiev.
Professor Eckhart Stratenshulte, the director of Berlin's European Academy, has his grumbles about the station (the links East are apparently as slow ever) but confirms that the German government is as keen as ever on the idea of a constitution for Europe.
"Germans think very much in terms of structures and constitutions, law and regulation," he says.
But he says that the impact of enlargement is changing the key alliances of EU.
"We have a very clear focus on Central and Eastern Europe... Germany sees Poland for example as a neighbouring country which is as important as France," he says.
With those words ringing in my ears, it's time to go to the Polish capital.
The train out of Germany is slower and older; with its timeless green cloth seats and compartments for six, it has more than a dash of faded romance.
Those on board are a bit more enthusiastic about the EU. Jobs and the environment top the list of things that people want tackling. Once again, the constitution elicits no interest whatsoever.
There is more enthusiasm for further enlargement; but you need to be careful to make sure you what kind of enlargement people are talking about.
"For Poland, enlargement really means Ukraine, it means maybe the Caucasus, maybe Georgia," says Krzysztof Bobinski, of the Polish Institute for International Affairs.
Polish enthusiasm for the EU is palpable. But as Pavel Swieboda, the head of the Foreign Ministry's European Union department, points out as diplomatically as possible, Poland's radically different recent history leads to a different perspective on how the EU should behave.
"We have a different perspective because our experience is different," he says.
"We want to be a competitive economy and open society. We don't have the burden of 50 years of integration on our shoulders."
Some countries in the EU may not have thought of integration as a burden. It's just one more reminder of how many views of the future of Europe there are.