Bordering Parque Nacional Palo Verde, this impressive facility is operated by a successful sugarcane family that has devoted 20 sq km to a wetlands refuge. In addition to hiking, biking and boat tours (some of which enter the national park), they also do a sugarcane demonstration; you'll make 'agua de sapo' (toad water) from lime, ginger and sugarcane.
Meals are served in the historic and atmospheric Casona (mansion).
The main entrance is about 15km south of Filadelfia. Head southeast out of town on Calle 5 and follow the signs. El Viejo can also provide transportation from anywhere on the northern Península de Nicoya.