any chance you could let us know about the derby games and the rivalries :-)
Hey I am not "Ruhr",
but from Germany as well (long time lurker, first time poster) and I will try to give you some sort of overview.
By definition derby is two teams from the same town playing each other, however that is pretty rare in German football.
Hamburg-St.Pauli, Bayern München -1860 München, Hertha BSC Berlin/Union Berlin/BFC Dynamo Berlin, FC Köln - Fortuna Köln, VFB Stuttgart - Stuttgarter Kickers, Chemie Leipzig - Lok Leipzig are the ones I can come up with straight away (might have forgotten the one or other), however the majority of the above mentioned real derbies rarely happen due to the teams playing in completely different divisions, so German Cup is pretty much the only possibility those teams meet up (unless St.Pauli and 1860 München get up to the top tier which is pretty unlikely at least in the case of 1860).
Besides the above mentioned "real derbies" there are a lot of rivalries in German football.
Best examples would be the notorious "Ruhr Derby" between Dortmund and Schalke. One of the biggest derbies in Germany with a lot of hatred on both sides. Both sides usually play pretty entertaining football as well, so its gonna be interesting on the pitch as well as on the terraces. :)
But lets start in the north with Hamburg vs. Bremen which is a pretty big rivalry due to both teams beeing located pretty close to each other. Hamburg lacks their inner city rival St. Pauli as they usually spend their time in the lower tiers of German football, so over the years some solid "hate" between Hamburg and Bremen has build up.
Next we got the "Rhein Derby(ies)" with the major one beeing 1.FC Köln versus Borussia Mönchengladbach.
Both clubs have been pretty successful in the past however they both spent a good amount of time in the second division as well and only Gladbach recently starts to live up to their former glory.
However they got a lot of followers in the Rhein Area and the clash of the "posh" citizans (Cologne) with the "farmer boys" from Gladbach is definitely worth a watch.
There is as well the small Rhein Derby with Cologne and Gladbach versus Bayer Leverkusen, however both Cologne and Gladbach consider that match up as the smaller of the Rhein Derbys especially as the fanbase of Leverkusen simply can´t match the passion/amount of fans of the other two bigger clubs.
Going down to the southern part of Germany there is the so called "Pfalz" Derby with Kaiserslautern versus Mainz. Its for sure a heated match up, however the majority of Kaiserslautern Fans considers the matches versus Frankfurt (now 2nd division) and Waldhof Mannheim (now 5th? division) to be the "real deal" simply because of Mainz not bringing any meaningful amount of away fans to Kaiserslautern and Frankfurt and Mannheim are definitely a different caliber in terms of vocal support and numbers.
Then we got Stuttgart versus Freiburg which is the Baden Würtemberg derby between "Schwaben" and "Baden" (people living in the southern/northern part of Baden Würtemberg), however same as of the previous mentioned derby the "real deal" would again be Stuttgart versus Karlsruhe (2nd division) and Freiburg is not really taken serious by Stuttgart.
Hoffenheim is a bit of a special case as its located in Baden Würtemberg as well, however the majority of German "die hard" football fans hate Hoffenheim as they only got to the top tier due to their "sugar daddy" Dietmar Hopp who build this team out of nowhere.
And especially the teams from Baden Würtemberg just ignore Hoffenheim and dont consider a match up versus them as "derby worthy".
Even further in the south we got the derby between Frankonia (FC Nürnberg) and Bavaria (Bayern Munich). Both teams coming from Bavaria however if you call someone from Nürnberg Bavarian he or she might get slightly pissed as the northern part of Bavaria considers themself as "Franken" and not "Bayern".
1 FC Nürnberg is the notorious underdog in those derbies, however they manage to beat the glorious FCB every now and then with a budget that is most likely 1% of what Bayern has on their hands to spend. :)
Pretty good atmosphere to be expected here as well, however if you want to visit a match and can choose I would pick Nürnberg at home. Nürnbergs home support is pretty good while Bayern away is much better than at home (less gloryhunters, more die hards)
Thats the current "big" rivalries in the German 1st division, however going down to the 2nd or even 3rd league has a lot of interesting games to offer as well and the support/atmosphere is sometimes even ahead of what the 1st division has to offer.
Let me know if you want more details. :)