Get ready for a truly unique Costa Rican adventure as you hike to the Rio Agrio waterfall. The trail, a relatively easy walk of about 1.5 kilometers, leads you through a stunning, lush canyon carved by the river itself. You'll notice the yellowish tones on the canyon walls, a result of the acidic water from the nearby Poas Volcano, which gives the 'Sour River' its name. The reveal of the waterfall is a dramatic moment, making for a memorable visit just a short walk from the entrance.