Nicolo and Antonio Zen were 14th-century navigators who, according to their 16th-century descendant Nicolo the Younger, voyaged all over the North Atlantic.
Nicolo the Younger's book was denounced as a fraud in the 19th century, but Andrea di Robilant makes a good case that the voyages were real and that the Zens reached the Shetlands, Iceland, Greenland and even Newfoundland, a century before Columbus sailed the Atlantic.
The book falls into two parts: the first third is essentially a history book, filling in the Zens' background, and it is rather slow going. On one page, I counted 51 proper nouns. The second part is a travel book, and as di Robilant retraces the Zen brothers' alleged voyages, searching for clues, it becomes much more absorbing.