Adventure stories date back to ancient times and revolve around a single, central, heroic character. Some adventure stories follow a group of heroes, such as The Three Musketeers. In an adventure story, there is always an event or series of events the hero or heroine must overcome to gain something or to survive. The hero is known as the protagonist, and the antagonist supplies the circumstances that the hero must overcome. Adventure stories move quickly and don't spend much time on the details of character or lengthy descriptions of history or background.
It's Dangerous Out There
The most significant element in an adventure story is danger. In great adventure stories, the protagonist is at risk throughout the story. Often an adventure story occurs while the protagonist is on a journey. When the hero conquers one danger on the journey, another one appears. In ancient adventures, the gods were often involved, making the danger to the hero a life-and-death scenario. In medieval times, adventure stories included romance in the dangerous mix as the hero was frequently at risk to gain the love of a lady.
This Doesn't Happen Every Day
A key element of adventure is that the perilous situation is new. The protagonist must find himself or herself in unknown territory. Science fiction uses this element best because the worlds involved are new to both the protagonist and the reader. The element of the unknown is one angle that raises the suspense in the story. For instance, if the protagonist has never been at sea and has to maneuver a ship in a storm, you have an adventure. If the story is about a seasoned captain of a ship enduring yet another storm, the suspense is diminished.
Just Do It
Literary novels often spend significant time on developing character through description. The opposite is true of adventure stories. Characters are defined in adventures by their actions and reactions in dangerous situations. How a hero reacts to a crisis through action is how that character is defined, not through any kind of internal investigation or rumination. Adventure heroes seldom spend time thinking because the level of danger in their story does not allow time for thinking.
Suspense and Surprise
In adventure stories, rising and falling suspense supply the pace of the story. As one conflict rises, another must be diminishing. To heighten the tension, the diminishing conflict can move slowly while the rising conflict continues to increase. Some element of surprise enters into the story when the audience comes to expect one action and another action instead takes place. The protagonist's unknown response to the surprise helps increase the suspense and continues to define the hero or heroine.