This is a type of relief produced in limestone, which is prolific in this area and caused by erosion. The rock dissolves due to constant contact with water and a series of superficial and subterranean forms are produced.

Karstic landscapes can be found on many of the routes in the region: the area surrounding “el Santuario de San Miguel”; closed valleys (Ata); depressions (“Campas de Albi”); caves (Alli and Aldatz); and chasms and springs where the underground streams reappear (the river Larraun, which has its source close to Baraibar, disappears underground and reappears again in Iribas).