This 9,154-hectare reserve, located on the interior side of the Valle de la Estrella, protects a remote and relatively unexplored area of rain forest. Trails through the forest are limited in extent, and tend to be very muddy. One of the best ways of exploring the reserve is to walk upstream along the riverbeds. Along the way, you may glimpse the strikingly patterned sunbittern, a bird that frequents tropical streams.

Huge colonies of Montezuma oropendolas and chestnut-headed oropendolas, large members of the oriole family with bright yellow tails, can be found nesting in the valley from January to August. Nest trees are easy to spot since they sport dozens of meter-long hanging pouch nests that the birds so expertly weave.

To get there: Just getting to the reserve can make for an interesting all-day adventure. From Limón, drive towards Cahuita and turn right at the sign for Penshurst (about 34 kilometers from Puerto Limón). About nine kilometers farther you will reach the extensive banana plantations of the Estrella River Valley, where navigation becomes a bit tricky and even claustrophobic as you drive for nearly ten kilometers through a seemingly endless maze of bananas (it's a good idea to ask directions of people you encounter). Once beyond the banana plantations, the dirt road begins to rise above the valley floor and offers some nice vistas. Four-wheel-drive is necessary for the final 14 kilometers to the reserve entrance.

Climate: Be prepared for rain. The daytime temperatures are warm, but given that the reserve is at an elevation of several hundred meters, it could get a bit cool if you are camping overnight.

History: The name of this reserve comes from the two main rivers that run through it, the Hitoy and the Cerere. These are names in the Bribri language which mean "moss-covered" and "clear waters," respectively.

The epicenter of the April 1991 quake that damaged much of the province, was located near the biological reserve which suffered numerous landslides and tree falls.