halsanefshellir cave made of basalt columns on reynisfjara black sand beach, iceland

arch basalt beach black sand cave cavern cliff coast column empty erosion europe formation frozen geology grass green halsanefshellir hexagonal haiexcl lsanefshellir iceland icelandic landmark landscape lava moss mountain myrdal natural nature people outdoor overgrown pillar reynisdrangar reynisfjara rock shore south stack stone tourism travel vertical view vik volcanic wall