The Vall de Boí is a narrow, steep-sided valley in the province of Lleida. It lies in the northeastern corner of the comarca of Alta Ribagorça, on the edges of the Pyrenees. It is the largest municipality of the region, with its main town being Barruera.The valley is best known for its nine Early Romanesque churches, making it the site of the densest concentration of Romanesque architecture in Europe. It was designated as a World Heritage Site by UNESCO on 30 November 2000. The valley also includes the highest ski resort in the Pyrenees, at Boí-Taüll, and borders the Aigüestortes i Estany de Sant Maurici National Park which lies to the northeast.