closeup of different forms of erosion on an irregular rock formation with grooves, furrows and moss

canyon cave cavern cliff concept ecosystem eifel environment erosion europe exploration forest formation geologic geology green groove grotto high hiking hill land massif massive mountain nature old outdoor park pattern plateau ravine reserve rock rocky rough rural sandstone stone summer surface texture tourism travel valley wall wild wilderness woods closeup forms irregular grooves furrows moss teufelsschlucht sunny day irrel germany