A week in Germany (maybe Austria and Germany too)

My friend and I are planing a trip to Germany in July for about a week, the only problem is deciding what the hell to do!

We are starting off in Frankfurt (I know someone who lives nearby) and then planing to head South to do some hiking/adventuring in and around areas like the Black Forest and maybe some of the typical south-of-the-Rhine villages and towns, and then maybe head to a few cities like Munich, Nuremberg and then ending in Berlin.

The only problem is deciding what towns to visit, what to do there and in these cities and whether we should book tickets for trains/buses in advance and for accommodation?

We both like hiking and the great out doors in general and I personally would love to experience the various urban centres and what they have to offer, but would very much like to avoid all the major tourist destinations if at all possible.

I'm not asking for anyone to plan this for me, but rather to give some much needed help and advice!

Thanks!