Castledown was a ruined city in Ice Henge.
Castledown lay in a deep valley running ten miles long, and five miles across. Trees covered the slopes forming a green ring. The ruins of the city covered the entire valley floor.
The city dated from before the Great Wars. It was virtually all made of metal. It did not seem to have been built to house people, but rather was better suited for warehousing or for factories, constructions or even storing machines.