Matienzo

Matienzo is the name of a village and a karst depression some 25 km southeast of Santander in Ruesga municipality, Cantabria, northern Spain. The limestone around Matienzo is riddled with caves (up to 58.6 km in length ) which have been extensively explored over the last 50 years by Spanish and British cavers.

the total length of cave passage explored, was 377 km.