The Ansó Valley is Aragón's western limit. Rich in fauna (mountain goats, wild boar, and even a bear or two), it follows the Veral River up to Zuriza. Towering over the head of the valley is Navarra's highest point, the 7,989-foot Mesa de los Tres Reyes (Plateau of the Three Kings), named not for the Magi but for the kings of Aragón, Navarra, and Castile, whose 11th-century kingdoms bordered one another here, allowing them to meet without leaving their respective realms. The Selva de Oza (Oza Forest), at the head of the Hecho Valley, is above the Boca del Infierno (Mouth of Hell), a tight draw that road and river barely squeeze through.
It's worth stopping at the pretty villages of Ansó and Hecho, where a preserved collection of stone houses are tightly bunched together along narrow cobbled streets overlooking the valley. In Ansó on the last Sunday in August, residents dress in traditional medieval costumes and perform ancestral dances of great grace and dignity.