Dolmen, or Hunebeds - (Huenenbetten ,Huenengraeber is the German name) is a name used for a large number of megalithic stone grave sites , large bolder stones set in formation around burial sites. Huenenbetten bolders were and are still remaining by the thousands in northern Europe all along the Baltic Coast lands .
Bolders were used partially underground to create chambers . Therefore also called chamber graves. A huge semi square , somewhat flat bolder was laid on top , for cover , giving it a mushroom-like appearance .
There are still many left today , even with the extreme density of population in Germany and all over Europe . An list of hunebeds (Huenenbetten) in northern Germany, made in earlier years by a landowner in Mecklenburg , showed over 1000 hunebeds at that time. I believe that was on Ruegen , an island in the Baltic Sea , off northern Germany.