Blood-curdling screams, strange voices and footsteps still terrify soldiers on guard during the late night "ghost shift" at the Castle of Good Hope.
The explanation, they are convinced, lies in the bloody history of the Castle and the restless spirits of those who were tortured there centuries ago.
To this day, soldiers who guard the Castle would rather walk all the way around the outside of the building than pass through the haunted archways in the wee hours of the morning.
The Castle was the centre of civilian, administrative and military activity at the Cape for 150 years and also the site of gruesome punishments, torture and executions.
The Castle is on Cape Town's ghost route - the buildings believed to be haunted, which people can visit to see for themselves if they dare.
Eerie stories have been told of footsteps pacing along the battlements between the two bastions of Leerdam and Buren; after World War Two, these inexplicable sounds were accompanied by a floating human shape without legs.
It is said this ghost could be that of a soldier who hanged himself in the bell tower 300 years ago.
There is also the ghost of a sad-faced woman, wearing a long, grey cloak, who walks through the Castle at night. Then there is the ghost who loves to join parties. It is said it could be Lady Anne Barnard, who lived at the Castle for five years from 1797 while her husband was colonial secretary.
Her ghost has been seen at functions in the ballroom, clothed in a ballgown of that era.
Guards and staff at the Castle insist there is more to the Castle ghosts than just "spook"stories.
Hilton Fredericks, who has done guard duty on the dreaded 2am to 4am shift, says bizarre things do occur in the small hours.
"One night a guard heard someone screaming for help and voices coming from the dungeon and torture chamber." When he went to investigate, there was no one there. But he felt a presence; his body became ice cold and the hair stood up on his arms and at the back of his neck."
He says some of the guards refuse to go past the Donker Gat (dark hole) dungeon when making rounds late at night because it feels as if there is a powerful force or a vacuum that wants to suck them in.
Some don't even want to use an alternative archway because footsteps can be heard on the cobblestones. Instead they walk right around the outside of the castle to get to where they want to be.
Fredericks adds that in 1952, a couple were granted permission to spend a night in the Castle during the Van Riebeeck Festival. During the night, they woke up to find a lance corporal waking up the soldiers. When they asked what he was doing, he said the bus drivers and bus conductors were protesting and rioting in the city streets.
The next day, when the couple tried to find out about the incident, there was nothing in the newspapers. They asked the staff what had happened during the night but no one knew what they were talking about.
Ashley Frantz, a tour guide and guard at the Castle, said when he first did the ghost shift in the 1990s, he had a frightening experience. It was pitch dark when he was walking through the archway near the Donker Gat dungeon late at night. A strange feeling came over him and he saw someone waving at him.
"I knew there were only two of us on duty and the other guard was on the other side of the Castle. I couldn't get out of there fast enough. I tore a piece of my pants and scraped my shin when I ran past barbed wire near the gate."
Abe Bergh, who has worked as a caretaker at the Castle for more than a decade, is another who has had experiences with the spiritual realm.
With fear evident on his face, he said one night when there was at a function at the Castle, he had to sleep over because there was no transport to take him home.
"During the night I felt this heaviness on my chest, and my body felt as if I was tied up. I couldn't move. Eventually I struggled free, kicking and screaming, and ran out of the room. I stayed awake until sunrise."
Karl Koperski, education officer at the Castle, often works late at night. "There is definitely a presence, sometimes it's an uncomfortable feeling. But you are definitely not alone; you are being watched," he says.