What it was.

After the fact, I've done some reading. Google is all that could help me out, so take it with a grain of salt if you want to, and I didn't dare ask any of the people at the time, but I feel like I should have gone back to the gate house and asked, perhaps, even if I would have felt a bit foolish.
So there's been reports of a woman's presence haunting the place going back centuries.
The exact spot where I was, I later found by looking at a map of the buildings, was near an old section of quarters for married couples, and close by a demi-bastion and the battlements overlooking the sea. This, it is said, is where she leapt to her death.