Interesting timing for this to appear, I've just started reading The Grand Tour (https://www.agathachristie.com/stories/the-grand-tour), from the blurb: "With a ten-month itinerary that would take her across South Africa, New Zealand, Hawaii and Canada, The Grand Tour is a unique record of Agatha Christie's round-the-world journey of 1922, told through her extensive and lively letters home to her mother."

So far I can confirm her letters to her mother are every bit as entertaining as her mainline literary work. It is absolutely crazy to me that she had this opportunity in 1922!