Following on The Lost Book of Adventure (2019) and presented in the same facsimile format, complete with images of stains, smashed bugs, and small attached botanical specimens, this engrossing diary records a five-week trip upriver—retracing a route from an old hand-drawn map (included as a glued-on foldout) with certain parts tantalizingly rubbed out. What lies in the missing bits? Readers will be as avid to find out as the unnamed and ungendered—but almost certainly European—“Unknown Adventurer” is. Accompanied only by Bibi, a female biologist friend with (fortunately, it turns out) excellent rainforest survival skills, the inexperienced narrator spends much of the arduous trek complaining: “This place isn’t endangered. We are.” But after many encounters with flora and fauna often as dangerous as it is unfamiliar to the adventurer, what lies at journey’s end turns out to be something wonderful, even more precious than gold…but, oh, so vulnerable too. Hundreds of colored-pencil drawings, done largely in blues and greens, accompany text printed in a faux hand-lettered but easily legible type. Sometimes quick and impressionistic, sometimes representational, their subjects include tiny insect specimens, broad landscapes and forest understories, portrait sketches of Bibi (a resident, and possibly Native, Brazilian) and the few locals they meet, and even inventories of camping gear. Keen identifies specific creatures and locales in discreet footnotes, and as “editor” adds comments fore and aft.