Berliner Mauerweg (along the former Berlin Wall) which is mostly paved and flat. Trail markings and instructions will be posted by organizers along the entire route.
It's always easier to train when you've got something in mind train for. Find an upcoming running event in your area and sign up, it's as easy as that. Train each week in preparation for the big day and then go out and have fun with it. You will have runners at all different levels of running abilities. You'll have semi pro runners right down to absolute beginners. Running is for everyone when you realise that the only person you're competing with is yourself - to gradually make those improvements and gains. Good luck on your journey.
Motivate yourself and your friends by downloading DOARUN - the worlds first interactive running game. Set up a running group and invite your friends to join.