In 1942, American Nobel Prize-winning physicist Arthur Compton pointed out that, “Because in this field of cosmic ray studies certain unique advantages are given by their geographical position, this field of physics has been especially emphasized in South America.” This paper seeks to interrogate the making of Latin America's uniqueness with respect to cosmic-ray research through an analysis that considers Compton's geographical argument, but also goes beyond it, referring to the interactions of nature, knowledge, practices, scientific communities, and diplomacy. To (...) begin with, it highlights the place-based strategies and practices associated with cosmic-ray research. Once research in the field at different altitudes demonstrated that cosmic rays traveled from outer space to the Earth surface, their nature was scrutinized by expeditions that covered broad vertical and horizontal expanses. The study of cosmic rays in Latin America displayed the mobilization of that strategy, which reinforced the reliability of certain sites located at high altitudes and close to the geomagnetic equator in projected investigations. Moreover, such analysis of cosmic rays involved research practices in the field, the emergence of (local, regional, or international) research traditions, and the creation of spaces of knowledge at different scales. By centering on the interaction of knowledge and place, this paper shows that an exploration of the “up-and-down journeys” of cosmic-ray research in Latin America expands our understanding of the geographies and practices of 20th-century physics. (shrink)