From Harry Potter and the Sorcerer's Stone:
"Three up... two across he muttered. "Right, stand back, Harry."
He tapped the wall three times with the point of his umbrella.
The brick he had touched quivered –– it wriggled –– in the middle, a small hole appeared –– it grew wider and wider –– a second later they were facing an archway large enough even for Hagrid, an archway onto a cobbled street that twisted and turned out of sight.
"Welcome," said Hagrid, "to Diagon Alley."
'out of sight' means not visible, but here the cobbled street seems to be appearing in front of their eyes. And 'that' here refers to the street, doesnt it? Then how can the street be 'out of their sight' in this scene? I don't understand this sentence.