That's the title of a most remarkable book about a most remarkable "adventure".
I have just completed Candice Millard's telling of Theodore Roosevelt's "Darkest Journey" down an uncharted, virtually unknown river in Brazil's Amazon rain forest. It's a must read.
The intrepid former president, with his son Kermit, a naturalist, a doctor, and several other notables, joined an expedition headed by a famous Brazilian military colonel, Candido Rondon, to explore "The River of Doubt" (Rio da Duvida). Its very existence unconfirmed, the river had never been run (to anybody's knowledge). Year--1914.

Beset with extreme weather, rapids and waterfalls, insects, illness, hunger, loss of canoes, murder, hostile Indians, etc., they finally made it, two months after push off. Roosevelt, himself became deathly ill, never fully recovering before dieing.

The adventure itself was sensational, but the informative scientific "sidebars" regarding the conditions and life along the river were interesting and enlightening.

Even if you're not a Theodore Roosevelt fan, it's a wonderful story and book. I had no idea this event ever occurred.