This idea is based on some video games, and inspired by currently changing seasons.

Map four distinctively different, neighbouring regions. They don't have to be located exactly in the corners, but should be approximately the same size. You can make each region represent a different season, or type of landscape; icy mountains with glacial lakes, lush grasslands, smelly swamps, tropical rain forests, chilly tundra, cactusy desert (cactusy is a word?). Each region can also be inhabited by different kinds of creatures or civilizations.

The goal is to create interesting contrasts that makes explorers want to wander the entire map and see all the sights! You can even invent entirely new types of landscapes!