Scout says that the Radley place had ceased to terrify her why

The Radley place had ceased to terrify her because she knew Boo was real and wasn't frightened of him any longer.

The Radley Place had ceased to terrify me, but it was no less gloomy, no less chilly under its great oaks, and no less uninviting. Mr. Nathan Radley could still be seen on a clear day, walking to and from town; we knew Boo was there, for the same old reason—nobody’d seen him carried out yet.