From the World Heritage inscription:
The cultural landscape of Madriu-Perafita-Claror Valley offers a microcosmic perspective of the way people have harvested the resources of the high Pyrenees over millennia. Its dramatic glacial landscapes of craggy cliffs and glaciers, with high open pastures and steep wooded valleys, covers an area of 4,247 ha, 9% of the total area of the principality. It reflects past changes in climate, economic fortune and social systems, as well as the persistence of pastoralism and a strong mountain culture, notably the survival of a communal land-ownership system dating back to the 13th century. The site features houses, notably summer settlements, terraced fields, stone tracks and evidence of iron smelting.
The Madriu Valley in Andorra is a beautiful and preserved region of one of the smallest countries in the world. Despite the size of Andorra, the Valley is large enough for a full day of hiking with the option of overnight staying in the mountains. The valley is still used for grazing by local farmers. If you do get a chance to visit Andorra take the time to go up into the valleys. The country may be small, but not so small as to preclude a wilderness experience.
View my complete list of UNESCO World Heritage Sites.