We went to Disibodenberg a few weeks ago, it was a ruins of a monastery from somewheres around 640AD. Very very cool, even the kids really enjoyed exploring the site. The 3rd grade archaeologist in me really loved this!
We also went to the Barfußpfad in Bad Sobernheim. The kids loved this- it was much more of a "hard core" walk than the one we did earlier this year. The fording of the river was lots deeper, and we were rain dodging too.