In 1996 a baby dwarf marmoset, later baptized Callibella humilis, was delivered to the author's doorstep. He could not have guessed that this moment would trigger a series of discoveries of unique, not yet identified animals and plants from the Brazilian Amazon. The indisputable existence of the second smallest monkey in the world somewhere out there in the vast Amazon Basin took the scepsis away from the scientist, convinced as Van Roosmalen was that discovering new primates at the turn of the 20th century would be really impossible. Describing mammals new to science is widely considered a privilege reserved to the great naturalists of the 18th and 19th centuries. Van Roosmalen's odyssey in search of the land of the Callibella revealed a river basin never visited before by naturalists, which was teeming with not yet described living things. A biological "terra incognita" that turned into a naturalist's el dorado. This book includes, among other amazing Amazonian stories, an account of Van Roosmalen's encounters with large-bodied, apparently overlooked creatures new to science that live up in the canopy, on the forest floor, as well as in the water of this Lost World the Rio Aripuana Basin. Here, we mention at least ten more big monkeys, giant peccary, fair brocket deer, dwarf tapir, dwarf manatee, a third freshwater dolphin cf. Pontoporia, giant paca, fair tree squirrel, pair-living red coati, red-coated tayra, Van Roosmalen's dwarf porcupine and hundreds of unknown trees and vines. In his account "Monkeys of the Amazon" (1854), Alfred Wallace based his evolutionary ideas on observations made during his long stay in the Amazon. In his river-barrier hypothesis he considered the Amazon Basin a huge freshwater archipelago in which the main rivers act as barriers to genetic drift. Through genetic isolation they provoke speciation. On his travels through the Amazon to study its biodiversity, Van Roosmalen noticed how right Wallace was 150 years ago and how well his hypothesis applies to the evolution and phylo-geography of living beings in the Amazon. He explains why it represents by far the highest biodiversity on Earth. Island bio-geography as defined for oceanic archipelagos can be perfectly applied to the interfluves of major rivers in the Amazon. Flying for hours over the never-ending sea of tree tops, people may think that the Amazon rain forest is just one 'sea of broccoli', all the same. But the over 100,000 plant species and millions of animal species (incl. insects) are not at all evenly spread across the Amazon. If so, this ecosystem would not contain the highest biodiversity on the planet. In this book it is explained for by a combination of factors: the tropical climate, the overall poor-nutrient soils on which the rain forest grows and has evolved over more than 70 million years, its unique geophysical history, its utterly complex mosaic of vegetation types, and the insulation caused by hundreds of rivers of three different water types together with their extensive floodplains. The latter do act as strong geographical barriers that prevent animals and plants to cross over from one interfluve to the other. Van Roosmalen's research confronted him with difficulties to lay one's hand on biological material without having to kill specimens to put in a museum. Political obstacles lay on his path, such as to collect and transport holotype material of new plants and animals for DNA analysis in a lab abroad. Unfortunately, time runs out. All these creatures are found at the verge of extinction. They all need their living space -the ancient Amazon rain forest- rigidly protected by law. Van Roosmalen 's popular-scientific book "Barefoot through the Amazon", a textbook on Amazon Rainforest Ecology and Biodiversity, will hopefully attract national and international public awareness. And draw attention to some of the most special and poorest known hotspots of biodiversity in the entire Amazon. They urgently need our protection!