Travelers moving south overland through Central America gradually have their choice of routes whittled away until they finally reach the end of the road in the swamps and forests of Darien, in Panamá, where the tenuous land bridge separating the two great American continents is nearly pinched out and the Pacific Ocean and the Caribbean Sea almost meet. Costa Rica lies at the northern point of this apex—a pivotal region separating two oceans and two continents vastly different in character.

The region is a crucible. There are few places in the world where the forces of nature so actively interplay. Distinct climatic patterns clash and merge; the great landmasses riding atop the Cocos and Caribbean plates jostle and shove one another, triggering earthquakes and spawning volcanic eruptions; and the flora and fauna of the North and South American realms—as well as those of the Caribbean and the Pacific—come together and play Russian roulette with the forces of evolution. The result is an incredible diversity of terrain, biota, and weather concentrated in a country barely bigger than the state of New Hampshire.

Lying between 8 and 11 degrees north of the equator, Costa Rica (50,895 sq km) sits wholly within the tropics, a fact quickly confirmed in the middle of a rainy afternoon in the middle of the rainy season in the middle of the Caribbean lowlands or Osa Peninsula. Elevation and extremes of relief, however, temper the stereotypical tropical climate. In fact, the nation boasts more than a dozen distinct climatic zones.