The world as active antagonist
Adventure fiction's most distinctive feature is its use of the physical world as the primary source of opposition: the mountain, the desert, the ocean, the jungle that actively works against the protagonist's progress rather than simply providing scenery. Writing the world as active antagonist requires specific knowledge of the specific environment — its particular dangers, its particular rhythms, the particular ways it punishes error — so that the challenges it presents feel like natural consequences rather than authorial invention. The river that rises after rain, the desert that disorients through featurelessness, the mountain that changes weather without warning: these are antagonists with their own logic, and the adventure that respects that logic feels more dangerous than the adventure that treats the environment as a stage set.