Rio Celeste, Natural park in Guanacaste, Costa Rica.

Rio Celeste is a park in the Guanacaste province of Costa Rica, about 130 km northwest of San José. It lies at 1,556 m on a ridge in the Tenorio volcanic massif, where the surrounding terrain is mostly hilly and wooded, with a higher summit of 1,832 m about 1 km to the northeast. The nearest town is Fortuna, 19.5 km to the west.

The land originally belonged to the Maleku indigenous people, who regarded the waterfall and river as sacred. Later, the area gained protection as a national park to preserve this natural site.

The blue colour is a mineral suspension of silicon, oxygen and aluminium that forms where two clear rivers meet. Guides along the trail explain the chemistry to visitors; the name Rio Celeste, "sky-blue river", comes from the colour itself.

The hike to the waterfall passes through rainforest with hanging bridges and many steps, requiring moderate fitness. Bring sturdy shoes and plenty of water to make the walk more comfortable.

Two clear rivers meet here with different chemical compositions, and their mixing creates the distinctive blue color through mineral suspension. This natural phenomenon is a rare geological example that few places on Earth can match.