Craved Kon-Tiki's salt-soaked gamble with nature's veto power from Thor Heyerdahl? River of Doubt by Candice Millard takes you deeper.

If Heyerdahl's raft taught you that the best expeditions taste like salt spray and existential risk, Candice Millard's River of Doubt delivers that same stripped-down confrontation with nature—only this time, Theodore Roosevelt trades Pacific swells for Amazonian rapids that don't care about your presidential résumé. It's the same audacious gamble, the same refusal of safety nets, the same testosterone-soaked camaraderie under conditions designed to kill you, except the jungle's canopy closes over your head and the predators circle from every direction.

Roosevelt's post-White House plunge into uncharted Brazil mirrors Heyerdahl's hypothesis-driven recklessness: a man testing bold ideas against nature's veto power, rewriting maps with sheer bloody-minded resolve while starvation and fever claw at his heels.

This is Kon-Tiki with piranhas instead of sharks—and no ocean to dilute the dread.