A vertiginous cliff or mountain is very high and steep. so high that you feel sick and dizzy (vertiginosus, from vertigo; VERTIGO)
having or causing a whirling sensation; liable to falling; "had a dizzy spell"; "a dizzy pinnacle"; "had a headache and felt giddy"; "a giddy precipice"; "feeling woozy from the blow on his head"; "a vertiginous climb up the face of the cliff"