Deuteronomy 12:13-14 God forbids His people to worship Him in high places, but solely in Jerusalem.

2 Chronicles 34 Manasseh\'s sins and unfaithfulness: built high places and set up Asherah poles and idols -- they are all connected together.

I think it probably was a Canaanite tradition to worship idols in the high places. Those places evoke the association of false-god worship -- condemned by God. It is indeed true that those people such as King Manasseh, built high places in addition to set up poles and idols.

We Christians are temples of God. We worship God in Spirit, and in the temple of God. The high places are still prohibited simply because by analogy they are our flesh, our own wills and thoughts.