Hidden in the northern region of Costa Rica, the Celeste River (Río Celeste) winds through Tenorio Volcano National Park with a color so vivid it seems unreal. The river’s striking turquoise hue is caused by a natural chemical reaction between two mineral-rich streams, Quebrada Agria and Río Buena Vista, which merge at a point known as "El Teñidero." This one-of-a-kind phenomenon creates the illusion that the water has been dyed blue, even though no pigments are present. Visitors can witness this optical effect firsthand from a bridge built just above the confluence.

Hiking through the surrounding rainforest is the only way to reach many of the river's highlights, including the famous Celeste Waterfall. The trail spans approximately 3.7 miles roundtrip, with steep sections, suspension bridges, and scenic lookouts. The waterfall plunges around 30 meters into a vividly colored pool, creating a dramatic contrast against the surrounding green forest. Along the way, hikers may spot sloths, toucans, poison dart frogs, or even tapirs if visiting early in the morning or during the rainy season.