Our bright blue raft starkly contrasts with the unremitting deep emerald rainforest that crowds in from both banks of the Rio Reventazon. The humid air is filled with the screeches of toucans and the unique grunt-scream utterances of howler monkeys, backdropped by the constant dull roar of a threatening stretch of pounding whitewater looming ahead. This 25-mile run through the Costa Rican mountains is providing us with continuous adrenaline-pumping rapids, couched in the middle of one of the most primitive and visually stunning rainforests in the world. We have pulled over on a gravel bar to catch our breath before the next big drop and I'm stretched back on the warm rubber tubes taking in the surrounding rainforest.

Rafters catching rapids on the Rio Reventazon

If you close your eyes and try to visualize a jungle river, your image would look exactly like the Reventazon. A fast-flowing, muddy riot of big rapids winding through the mountainous highlands of Central America, the Reventazon blends spectacular tropical scenery with challenging whitewater.

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High mountain bluffs spread back from the river, offering vistas of 200-foot-tall Ceiba trees with monkey vines hanging from each branch. Large elephant-ear plants — called"poor man's umbrellas" locally — shade gigantic bromeliads, palm trees, and ferns. River otters ply the eddies and backwaters of the river. Three-toed sloths, spider monkeys, and huge three-foot iguanas are silhouetted against the leafy jungle canopy. The rainforest moves to the flights of brilliant blue butterflies, multicolored exotic birds, and showy white egrets. The bright red and yellow fruits and flowers of heliconias, orchids, and dozens of exotic plants add to the mesmerizing mix. Crystal-clear waterfalls magically materialize from the green depths along the riverbanks.