▁They ▁are ▁usually ▁made ▁from ▁rocks ▁with ▁wood . ▁ ▁O vo os ▁are ▁often ▁found ▁at ▁the ▁top ▁of ▁mountains ▁and ▁in ▁high ▁places , ▁like ▁mountain ▁passes . ▁In ▁modern ▁times , ▁some ▁of ▁them ▁have ▁developed ▁into ▁large ▁and ▁elaborate ▁structures , ▁becoming ▁more ▁like ▁tem ples ▁than ▁simple ▁alt ars . ▁ ▁They ▁serve ▁mainly ▁as ▁sites ▁for ▁the ▁worship ▁of ▁Heaven ▁and ▁less er ▁gods ▁led ▁by ▁sh am ans ▁and ▁k ins ' ▁el ders , ▁but ▁also ▁for ▁Buddh ist ▁cer emon ies . ▁ ▁In ▁custom ▁When ▁travel ing , ▁it ▁is ▁custom ▁to ▁stop ▁and ▁circle ▁an ▁o vo o ▁three ▁times , ▁moving ▁clock wise , ▁in ▁order ▁to ▁have ▁a ▁sa fer ▁journey . ▁Usually , ▁rocks ▁are ▁picked ▁up ▁from ▁the ▁ground ▁and ▁added ▁to ▁the ▁p ile . ▁Also , ▁one ▁may ▁leave ▁offer ings ▁in ▁the ▁form ▁of ▁swe ets , ▁money , ▁milk , ▁or ▁v od ka . ▁If ▁one ▁is ▁in ▁a ▁hur ry ▁while ▁travel ing ▁and ▁does ▁not ▁have ▁time ▁to ▁stop ▁at ▁an ▁o vo o , ▁hon king ▁of ▁the ▁horn ▁while ▁passing ▁by ▁the ▁o vo o ▁will ▁suff ice . ▁ ▁In ▁ceremony ▁ ▁O vo os ▁are ▁the ▁site ▁for ▁Heaven ▁worship ▁cer emon ies ▁that ▁typically ▁take ▁place ▁at ▁the ▁end ▁of ▁summer . ▁Wor sh ipp ers ▁place ▁a ▁tree ▁branch ▁or ▁stick ▁in ▁the ▁o vo o ▁and ▁tie ▁a ▁blue ▁k had ag , ▁a