Hello All ,
Coming this September I have some 4 weeks of time off to spend on a tour across Europe. Weather permitting, the mountains of Czechia and Slovakia along the German and Polish border are looking like an alluring proposition.

Judging by the view on Google Earth Germany will be best crossed as quickly as possible and I'm set on avoiding the autobahn and taking the country roads. Entering around Rheine (north of Munster near the Dutch border) and with sights set on Hof (German Czech border) there's what looks like a hilly ridge running between Kassel and Hof.
1) Would this possibly be the most fun ride to get there (disregarding a strenuous detour along the German Alps)?

Once in Czechia I'm hoping to reach the Slovakian - Ukrainian border via the foothills of the mountain ranges running along the north of Czechia and Slovakia, or at least avoid some of the steeper climbs (not a fan of great heights but usually a necessary evil to get to the twistier paths).

During three earlier bike trips I've ventured into Spain via France using Google maps as guidance across mountain ranges to the routes recommended in "Great Motorcycle Tours of Europe" while explicitly avoiding highways but often times it would lead me over plain provincial roads. Is the subscription to the iPhone app "Scenic" recommended to route me away from bland roads or should I bite the bullet and purchase an Garmin Zumo XT2? (2)

On the topic of "Great Motorcycle Tours of Europe", it recommends riding north of the Czech border on the Polish side in what seems to be flatter country - Wroclaw to Krakow and then on to Poprad. Is this parallel route preferable to the Mountains just below it? (3)

Thank you for your thoughts.

The important thing to understand about Germany is that the majority of it is VERY densely populated - it's not nearly as urbanized as some other rich countries, with most of the population in the cities and empty countrysides. So local roads in Germany may or may not be plain, but they are very likely to be very busy with local village traffic, and therefore not fun to ride on. This is defintiely true of the Ruhrgebiet, the historically industry-heavy area around Cologne-Düsseldorf-Dortmund that is pretty much a single large urban area with super heavy traffic. You probably won't find any good riding roads until you get to the Harz in central Germany, then you can veer down to Dresden (worth a long lunch stop for the stunning town center) and continue into the "Saxon Alps", through Bastei and Hrensko - that's good mountain valley times.

Honestly though, don't expect to be out of bumper-to-bumper local traffic until you get to the High Tatras. The Germans built the autobahn for a good reason, and that reason was that getting anywhere on local roads is a pain.

The autobahns are a mixed blessing. When they're clear they're great, but they draw an awful lot of traffic and some of the worst staus (jams) I have seen in all my life have been on the autobahns around Stuttgart. Filtering is illegal in Germany so if you can avoid the queues in the first place it's good. Whichever route you choose you may find Sunday is a good day to travel, as LGVs are banned from the roads that day. Note, autobahns are very sparsely supplied with gas stations.

I've been in pretty bad ones around Hamburg in particular, but nothing compared to the Milan-Bologna autostrada. Filtering may be illegal, but in practice if the cars are literally stopped, and you don't cross over into the shoulder that's reserved for emergency vehicles, I doubt very much that you would get into real trouble.

Of course, if there's an autobahn traffic jam, the local roads are likely also jammed with people trying to get onto the autobahn...

Thank you for your thoughts TomKat and AnTyx.

The Ruhr I will most definitely be avoiding as the Autobahn. I just can't stand the noise when doing highway speeds despite buying the best ear protection the store had on offer and a Schuberth C4 helmet.

Dresden looks gorgeous but city trips will be saved for when I have switched to a set of lockable panniers.

If the weather outlook does turn miserable Croatia is on the cards though that will leave me with an even longer sprint across Germany.

As AnTyx said I would drive through the Harz ¨mountains¨ and then on your way you could stop and see the Göltzschtalbrücke and the german-german border museum near Mödlareuth, if you should find them interesting. Also if you have time their are some nice things to see in the Harz. I also transit Germany on most trips but I always try to find some interesting places to make a nice route and to see something on the way to destination.
As mentioned before don´t skip the Sächsische Schweiz (Bastei) south-east of Dresden.

Not in my experience. Not only did I get pulled and fined for filtering on my way to Garmisch-Partenkirchen, but the police were trying to get my BMW R1200GS off the road on the basis I was running TKC80s and these were not authorised fitment.

Fortunately I was able to pull up the UK Motorrad site and show the police they were an option at the time of purchase.

__________________
"For sheer delight there is nothing like altitude; it gives one the thrill of adventure
and enlarges the world in which you live," Irving Mather (1892-1966)

Thanks for the recommendations, I will definitely keep those in mind!

Are the Harz mountains preferred of the Kassel to Hof stretch south of Harz (Thuringian Forest)?

Difficult question because I don´t know what you prefer. I have never been in the Thüringer forrest, only passed it on the autobahn.
As I see it the Thüringer forrest is not as mountainous as the Harz, so the question is do you want more forrest or mountains.
On the other hand, you said you come in from Holland, if you live in Holland or nearby you could easily do a seperate trip to the Harz some day as it´s not far from the dutch border. Then you could do the Thüringer forrest on your planned trip to Czechia.
Another tip: since sometime this year Germany is finally visible in Google maps street view so you could get a better idea of how it looks like.

Have a safe and nice trip.

The mountainous roads will be more fun and judging by the photos on Gmaps they're not too high to seriously slow things down but as the leg through Germany will be pricey staying overnight I hope to be spending no more than two nights there before reaching Czechia. The stretch beyond Harz is seemingly quite plain so I will probably opt for the Thüringer forrest, it should stop riding from becoming dull.

Thanks I'd share some photo's but the web is already inundated with photos of bikes in hilly scenery.