Cape Sunion Prison (ケープスニオンの監獄, Kēpu Sunion no Kangoku) is a watery prison overlooking from a wall of the tall cliff at Cap Sounion, used to imprison the captives of the war of the gods. It is said (and soon proven wrong) to be so strong that it needs someone of divine power to break free. Behind the rear wall of the confinement, in a rocky chamber with no apparent access, holds Poseidon’s Trident sealed by Athena.
The barred window of the prison overlooks the sea, and is placed just above water level when the tide is low. When the tide is high, sea water can flow through the bars and overflow the confinement. Although this does not kill the prisoners, it is a very gruesome torture.
Gemini Saga uses this place to imprison his twin brother, Gemini Kanon for his brother's evil and for trying to sow darkness within him.
In Saint Seiya Omega, after the defeat of Mars, Gemini Paradox was locked in this place.