it's a place where once, a Celtic group had built a settlement, one of the largest and oldest of the region.
i've been to before once, in winter, and first didn't find it. now it was easier.
there's a celtic walkway, which leads around the settlement area in a loop -
walking the loop would take about 27 Kilometres / 6 hours.
here are some impressions and maps from the web, the first image shows the rather safe and island-like place of the settlement: on the plateau, above a stone cliff:
(here is more on a webpage "Heidengraben" ( in german)
it's always special to walk those ways, knowing that thousands of years ago, people walked there already, so close from here, and so far away in time.
and here's the blog post and an image of the first visit: 2200 years ago, near here