Where to find: Extreme north of Burgos. Surface:3.400Ha. Relief: limestone situated on the Meridional side of the Cantabrian Range. The river “Guareña” enters the clump creating the Karstic Complex of Ojo Guareña. Its nearly 100 kilometres of length makes it the most important complex in Spain and one of the ten largest ones in the world.

Vegetation: There are plenty of evergreen oaks and Portuguese oaks. Inside the cave you can find algae, fungus and bacteria.

Vegetation: a lot of birds of pray: Griffon vultures, Egyptian Vultures, wild boars, foxes and wildcats. Inside the cave there were discovered 63 species of cave invertebrates of which four are unique.

Protection figure: Natural monument

Information available: Antique Tourist information office of Frias (Burgos) Tel: 947 358 587

Access: from Espinosa de los Monteros, Cornejo and Cueva.