He recalled an old line or two, from Walter Scott, he thought; And he bowed his pride To ride a horse-boy in his train.
As he remembered it, the service had a motive somewhat similar to his own, and he was glad to "bow his pride," because he believed that he would have ample chance to raise it up again.

As he went about his work singing and whistling softly to himself, he cast many a glance up at the huge castle.
Truly Zillenstein had been a great fortress.

In the old days it must have been impregnable.

Much of it was still standing in its ancient strength.

John saw that the walls were many feet thick, and that in the older parts the windows were mere slits through which a human body could not pass.
A much more modern addition to the right wing had been built, and John surmised that Prince Karl and his suite lived there.