Castle Downs is a dome-shaped hill, 216 metres (709 ft) high, located in mid Cornwall, UK.

[2] There is a major hillfort, Castle an Dinas, on the summit and extensive and panoramic views across the county to both north and south coasts.

About 1½ miles to the east is the sister hill of Belowda Beacon (227 m).

[4] The major summit feature of Castle an Dinas is a massive Iron Age hill fort comprising 3 concentric ramparts and ditches that were probably originally surmounted by wooden palisades.

The hillfort has been partially damaged by a, now closed, 20th century wolfram mine.