This book, published in 1997, in 5 chapters describes the 5 journeys made by Jesuit explorers between 1624 and 1721 to Tibet, then terra incognito.
This story is largely unknown. To Caraman’s credit he had researched Jesuit archives in Rome and original letters written by these explorers.
While there are no endnotes this book had reproduced 5 maps showing the 5 journeys.
If your interest is on the early exploration of Tibet, you should also read A Stranger in Tibet by Scott Berry about a Japanese Zen monk who trekked to Tibet in 1900.