With Germany pretty much sitting in the middle of Europe, I've spend most my time visiting our various neighbors. Traveled to the Netherlands, Belgium, France, England, Austria etc. I think the longest road trip I had was when we were visiting the County of Kladsko in Poland. That area used to be a part of Germany before the outcome of the second world war and it is where my relatives on my father's side are from. His parents had a farm there with my grandpa raising horses. The farm actually still stands (or stood when I last was there) and the people living there today where nice enough to allow us a short walk over the grounds and taking some pictures.
Distance wise it wasn't that much, the longest individual trip probably just scratching the mark of around 800km or 500 miles. But I got a pretty nice view of what surrounds me.