From the introduction:
HYPERBOREA is a role-playing game of swords, sorcery, and weird science-fantasy.…the players create player characters (PCs), including fighters, magicians, clerics, and thieves.
The heroes of a HYPERBOREA game delve dungeons filled with horrifying monsters, lethal traps, and bewildering puzzles; they explore savage wilderness frontiers and dangerous borderlands; they probe ancient ruins and investigate cursed tombs; they match steel against sorcery and sorcery against steel; and they plunder for gold, gems, and magical treasure.
HYPERBOREA is a “flat earth” realm hemmed in by the mystical boreas (“North Wind”), and under the scarlet light of a bloated, dying sun, its roiling seas spill eternal over the world’s rim. This world is in a perpetual state of decay and is populated by disharmonious men and women, hostile monsters, and weird, alien beings.