The Foster-Sisters by Lucy Ellen Guernsey

I SHALL never forget my sensations when I felt myself fairly outside the convent walls. Though I had lived in France sixteen years and more, I had never seen more of it than was visible from the window of the little room over the porch-the only one to which we had access which opened on the outside world. How different the building looked from the outside. I had never even known of the existence of the two round towers at the outer corners, since only their pinnacles were visible from the court, and these I had always supposed to be on the roof itself.

"Why, Amabel, did you know those towers were there? " I exclaimed.