▁the ▁territory ▁of ▁the ▁city ▁of ▁Dort mund , ▁the ▁Ar de y ▁Hills ▁descend ▁gradually ▁into ▁the ▁plain ▁of ▁the ▁ ▁West phal ian ▁Low land ▁in ▁the ▁area ▁of ▁Mün ster land . ▁To ▁the ▁south ▁and ▁west ▁they ▁are ▁bounded ▁by ▁the ▁River ▁Ru hr , ▁their ▁rug ged ▁s lop es ▁often ▁dro pping ▁ste ep ly ▁into ▁its ▁valley . ▁On ▁those ▁s lop es ▁the ▁point ▁where ▁there ▁is ▁the ▁maximum ▁ 1 6 5 . 2   m ▁height ▁difference , ▁from ▁the ▁upper ▁storage ▁bas in ▁( ca . ▁) ▁to ▁the ▁H eng st ey see ▁( ), ▁is ▁used ▁by ▁the ▁p ump ed - storage ▁power ▁station ▁of ▁Ko ep chen werk ▁in ▁Her de cke ▁to ▁generate ▁electric ity ▁from ▁hyd rop ower . ▁ ▁S ett lement s ▁ ▁The ▁following ▁cities ▁and ▁towns ▁are ▁located ▁in ▁or ▁at ▁the ▁Ar de y ▁Hills ▁along ▁the ▁Ru hr ▁− ▁from ▁east - n ortheast ▁to ▁west - s outh west ▁− : ▁Fr ö nd enberg , ▁Un na , ▁Holz wick ede , ▁Sch wer te , ▁Dort mund , ▁Her de cke , ▁W etter ▁and ▁W itten . ▁ ▁E lev ations ▁ ▁The ▁highest ▁point ▁in ▁the ▁Ar de y ▁Hills ▁is ▁the ▁long ▁r idge ▁of ▁Auf ▁dem ▁Heil , ▁which ▁r ises ▁in ▁the ▁territory ▁of ▁Her de cke ▁west ▁of ▁the ▁town ▁itself . ▁This ▁and ▁the ▁other ▁high ▁points ▁in ▁the ▁Ar