I agree that this is impossible to envision.

Firs there is the politics

 Germany lack the political will to confront Russia over almost anything due in a large part to the country?s dependence on Russian Natural Gas.  Merkle has practically had Putin?s c@ck in her mouth over issues like expanded NATO membership and Georgia.

Lack of popular will. Germany is one of the last Western Powers that still has military conscription and about 30% of the population declares themselves has conscientious objectors.  There is hardly  enough of a war like attitude to support an invasion of Eastern Europe.  Heck you cannot even get popular support for a force in Afghanistan.

Military.  Germany is better equipped on a per item basis than Russia but they do not have a big enough military and lack the force projection/logistics capability on their own to support an invasion of Russia

This is the only way I can think of where a conflict between these nations occurs:

If there were to be a confrontation with where Russia would face Germany on vaguely the same front as before it would be over Ukraine. Ukraine is increasingly becoming independent of Russia while Russia feels that Ukraine should essentially be a province of a Russian empire. Dmitry Medvedev recently wrote an open letter condemning the current unpopular leader of Ukraine in a bid to influence the election- I am trying to remember the name of the man who said "Without Ukraine, Russia is not an Empire, with Ukraine, Russia is automatically an Empire." or words to that effect.

I know he was in the US state department and was fairly well respected but I can't find the article.

Germany and the other EU powers want a strong independent Ukraine as a counterweight to Russia and as an alternate source of gas- I think they just finished another pipeline through Ukraine, but again I'd have to goal and find the article.

Now after Georgia, we have precedents for Russia using force to knock it's satellite states into line.

Ukraine may be a much more formidable prospect than Georgia- but the Kremlin doesn't think in these terms- they're too used to getting their own way.

So it's conceivable that some move of further independence could prompt Russia into finding a pretence to attack Ukraine.

Ukraine applying for EU or NATO membership would be a good one. Let?s say EU membership since the Kremlin isn?t stupid enough to pick a fight with the US.

Now the question is- do Germany and her EU allies have the balls to intervene?

The Kremlin will never attack if they believe the answer is yes because then they're fighting Germany, Ukraine, and Poland for starters before we decide what  the Scandinavians will do- let alone Britain which could depend on gas for 70% of demand soon, or France- the whole EU could join in. It?s not cost effective.

So if Russia attacks it will do so believing the EU powers will not have the temerity to intervene.

For there to be a war at all, Russia has to have miscalculated dramatically. I believe this is possible as the Russians may mistake the European preference for using ?soft power? rather than overt military intervention as opposed to other great powers for cowardice. One can imagine ?We shall not go gently into the night? style speeches being made in Warsaw and Berlin- because if the Kremlin is allowed to essentially annex one sovereign nation- where will it go next? It will go west and attempt to reassert it?s spheres of influence in Eastern Europe and the Caucasus.