Costa Rica lies between latitudes 11°13’N and 8°N and between 82°33’W and 85°58’W, in the middle of the Tropic of Cancer. Among Costa Rican territory is Isla del Coco, an island of 10 square miles (25 km2) in the Galapagos chain about 300 miles (480 km) southwest of Costa Rica, where Captain Morgan’s treasure is said to be buried. Because it is a tropical country, there are only two seasons (sometimes indistinct), the wet and the dry. In some parts of the country the seasonality is more accurately divided into the wet and the wetter.

Costa Rica is bordered to the north by Nicaragua and to the south by Panama. Together, the countries of Central America make up the Isthmus of Panama, a narrow ridge of land joining the North and South American continents and dividing the Atlantic and Pacific Oceans. Although it is only 19,652 square miles (50,900 km2) in area (about the size of West Virginia, Nova Scotia or Switzerland) and no wider than 175 miles (280 km) at any point, Costa Rica is very geographically and biologically diverse.
Costa Rica lies on the Ring of Fire, a 9,000-mile (14,500 km) line of tectonic plate boundaries running from Alaska to Tierra del Fuego, characterized by earthquakes and volcanoes. The land that is now Costa Rica was underwater ten million years ago. The Cocos plate moved northeast and collided with the Caribbean plate, causing it to uplift (known as subduction). This land continued to be driven upwards, first piercing the ocean’s surface at what is now the Peninsula of Nicoya. This intense geologic activity was accompanied by earthquakes and volcanic eruptions, which added to the land height.

For several millennia a string of islands, probably mostly the tallest volcanoes, linked North and South America. About three million years ago, the activity of the subduction zonefinally formed a continuous land link between the continents and separated the Pacific Ocean from the Caribbean Sea. Four mountain ridges unite to form the highlands dividing the Pacific and Caribbean plains: Cordillera de Guanacaste, Cordillera de Tilarán, Cordillera Central and Cordillera de Talamanca (from north to south).

These mountain ranges are composed of extinct and seven active volcanoes such as Cerro Chirripó, which at 12,526 feet (3,818 m) is the highest peak in the country, Volcán Arenal 5,358 feet (1,633 m), considered by many volcanologists to be the most active volcano in the Western Hemisphere (it is constantly spewing ash, vapor and molten lava) and Volcán Poás, which has a mile wide caldera, the largest collapsed crater in the Western Hemisphere. Even atop Costa Rica’s highest mountains, paleontologists are continually discovering fossils of sea creatures, proof that the Isthmus of Panama was once underwater.

Four of the nation’s five largest cities are found in a high plateau in the central highlands (Meseta Central): Alajuela – home of the Juan Santamaría International Airport, Heredia – the university center, Cartago – the former capital, and San José – the current capital and largest city. Nearly two-thirds of the country’s population lives in this area, which lies at an average of 5,000 feet (1,524 m) above sea level. The land plunges down the volcanic slopes northeast into the vast Caribbean plains and to the smooth coastline, which stretches 132 miles (212 km) in length. The lowlands on the Pacific side are far more rugged, characterized by rocky streams and cliffs. The huge Peninsula de Nicoya in the north and the smaller Osa Peninsula in the south make the ragged Pacific coastline 631 miles (1,016 km) in length.