Been twice & speak the lang.
Its one of those places where there isn't really one "must see" thing...but pretty much every little town has a ton of history & culture. So its very much dependent on you whether that works for you. So generally the history fanatics do better than the rest.
Obviously also a very modern country...but that manifests itself more in a subtle "sht just works" fashion rather than as a must see location / event.
Check out the Rhein / Rhine area...there are a billion castles there (trade route in the past so every local wanna-be prince built a castle on the shore to exert power.
If Christianity is your thing then there might be some specific locations to visit though @ Luther. e.g. Schloss Wittenberg
>"must do" things
Maybe try out the no-speed limit Autobahn.(NB not all routes are speed limit free...)
Also check out the bulk train tickets...you get tickets valid for X days that cover a bunch of routes...can work out well for tourists.
Advice...you'll be fine...as I said "sht just works" and everyone below 30 can speak English anyway.
Personally I'd head towards the south...its a little more "exotic" plus seeing how you'll need a Schengen Visa anyway you can easily hop across a border. Else the German / Netherland border towns have a certain quaintness to them too (and hybrid culture due to border disputes in the past)...excellent for cycling too.
