The River of Doubt:Theodore Roosevelt's Darkest Journey by Candice Millard

In 1914, following a failed attempt to get back into the Presidency, Theodore Roosevelt decided to explore an uncharted tributary of the Amazon - the River of Doubt.  He and his entourage, which included his son, encountered unfriendly natives and unnavigable rapids. They battled malaria and near starvation.  It was an amazing journey.  But another part of the story was the strength and character of Roosevelt himself.  Whatever you think of his politics, there is much to be admired about him in this epic tale.