When they walked to the front of the Castle, they stood overlooking the Castle again. They know this is the castle of the Castle, the locals prefer to mention frequently that there is something in it, but no one knows what's.
When they walk up to the castle. They stood at the castle again. They knew that the castle. Castle is where the locals like to mention frequently that there's something in it. But no one knows what that is.
When they reached the front of the castle. They stood looking at the castle again. They know this castle. The castle that people likes to talk about is often that something in it. But no one knows what.