In Search of the Great Unknown: 20 Science-Fiction Adventures surveys the formative energies of speculative fiction, assembling voyages beyond Earth, technological marvels, occult-inflected mysteries, lost-world romances, and encounters with altered futures. Its range extends from Gothic atmosphere and sensational adventure to proto-scientific extrapolation, imperial romance, and planetary imagination. Standout modes include lunar and interplanetary travel, catastrophic invention, and explorations of hidden civilizations, revealing how early science fiction transformed contemporary discoveries and anxieties into narratives of wonder. The contributors-among them internationally influential pioneers, popular adventure writers, journalists, and experimenters in fantastic fiction-represent the heterogeneous literary culture from which modern science fiction emerged. Their works belong to the nineteenth- and early twentieth-century convergence of scientific popularization, colonial-era exploration narratives, utopian speculation, and Gothic revivalism. Read together, these voices illuminate the genre's development across national traditions and publishing forms, while demonstrating that the "unknown" could serve as a site for debating progress, power, fear, and human possibility. This volume is especially rewarding for readers seeking both pleasure and historical perspective. It offers an accessible course in science fiction's prehistory, inviting comparison among distinct styles, ambitions, and imaginative geographies. Students, scholars, and adventurous general readers alike will find a rich dialogue between its tales, as each enlarges the others' vision of what speculative literature could dare to imagine.