This neon blue river gets its color from a unique mix of bacteria and volcano minerals.
Along the river there are multiple hot springs and an impressive waterfall, all the same, seemingly unnatural blue. Pictures of the waters are regularly accused of being photoshopped or invented, but the simple chemistry in the river’s depths is very real, as countless hikers experience each year.
Rio Celeste is located within the Tenorio Volcano National Park. The closest airport is Liberia International Airport. Many of the surrounding guesthouses/hotels have walking paths that lead directly to Rio Celeste (typically 1-2 miles). Some of guesthouse/hotel trails can be closed due to inclement weather, but the park's main entrance is usually reliable. Entrance for non-residents is $12. A 4x4 is STRONGLY recommended for getting to the park entrance, and for Costa Rica in general.
Locals will try and convince you to rent galoshes at the entrance, but you will be fine in sensible shoes.
Clancy's comment: Wow. I'd love to see it.