The plot of A Link to the Past focuses on Link as he travels on a journey to save Hyrule, defeat Ganon and rescue the seven descendants of the Sages. A Link to the Past uses a 3/4 top-down perspective similar to that of the original The Legend of Zelda, dropping the side scrolling elements of Zelda II: The Adventure of Link. A Link to the Past introduced elements to the series that are still commonplace today, such as multi-level dungeons, new weapons and items as well as the Master Sword and the concept of an alternate or parallel world.
A Link to the Past is the first appearance of what would subsequently become a major Zelda trademark: the existence of two parallel worlds between which the player travels. The first, called the Light World, is the ordinary Hyrule where Link grew up with his uncle. The second is what was once the Sacred Realm, but became the Dark World when Ganon acquired the Triforce. The Dark World is a corrupted version of Hyrule; the water is a dark, unpleasant green color, the grass is dead, skulls replace rocks and pots, and trees have faces. People change forms in the Dark World based on their nature; without an item to prevent it (in this case, the Moon Pearl), Link turns into a pink rabbit. Each location in the Light World corresponds to a similar location in the Dark World, usually with a similar physical structure but an opposite nature (e.g. a desert in the Light World corresponds to a swamp in the Dark World, a peaceful village in the Light World corresponds to a dilapidated town of thieves in the Dark World).
Link can travel from the Dark World to the Light World at almost any outside location by using a magic mirror, and can travel back to the Dark World again from the same location using a temporary portal left behind on the map at the point where he reappears in the Light World. Otherwise, Link must use hidden warp locations throughout the Light World to travel from the Light World to the Dark World. Travel between worlds allows for puzzles in A Link to the Past that exploit structural differences between the Light and Dark Worlds, as Link may travel to otherwise inaccessible areas in one world by warping from parallel but accessible locations in the other world.