From the introduction:
Astonishing Swordsmen & Sorcerers of Hyperborea (AS&SH) is a role-playing game of adventure played with paper, pencil, dice, and imagination. Participants include one referee and one or more players. The referee prepares and presents the adventure material, including the circumstances, challenges, quests, and mysteries faced, and the players create player characters (PCs), including fighters, magicians, clerics, and thieves. The heroes of an AS&SH game delve dungeons filled with horrifying monsters, lethal traps, and bewildering puzzles; they explore savage wilderness frontiers and hostile 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 the default campaign setting for Astonishing Swordsmen & Sorcerers of Hyperborea. This “flat earth” realm is 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. Hyperborea is in a perpetual state of decay, populated by disharmonious men, hostile monsters, and weird, alien beings. Hyperborea is an adaptable campaign setting that can be used independently or in conjunction with other milieux, published or homebrewed; indeed, Hyperborea might be just beyond the North Wind of any campaign setting.