As the story goes, Douglas Adams was lying in a field in Innsbruck, drunk, when the idea that evolved into Hitchhiker's Guide to the Galaxy first came to him.

The Guide is a galactic guide, which had become popular everywhere but on the planet earth.  Arthur Dent wakes up one morning to discover that his house is about to be imminently demolished and replaced by a bypass.  He goes to a bar, and meets the Guide's earth correspondent, Ford Perfect.  Whereupon he discovers that the Vogons, integalactic bureaucrats, intend to destroy the entire planet and replace it with a bypass - a hyperspace bypass.

Whereupon begins the intergallactic travel, and explorations ranging from planets to questions about brainwaves, Arthur's in particular, and a search for the Answer, as well as the Question.