What does Conway consider the ‘'crowning astonishment'' of the day? (Chapter Five)

The harpsichord and modern piano were the "crowning astonishment" of the day.

“Pretty little place,” commented Barnard, as Chang led the way into an open pavilion which, to Conway’s further delight, contained a harpsichord and a modern grand piano. He found this in some ways the crowning astonishment of a rather astonishing afternoon.