About 8 km northeast of Guernika, in the Urdaibai biosphere, the Santimamine cave contains a small but exceptional series of Palaeolithic paintings: bison, horses, deer, and a bear, dated to around 14,000 years ago and stylistically related to the better-known art at Altamira.
Direct access to the painted chamber has been closed since 2006 to halt the spread of fungal growth. Visitors take a guided tour of the cave's outer galleries — geologically impressive in their own right — followed by a high-resolution 3D film of the painted hall. Tickets are timed; book ahead in summer.