From the World Heritage inscription:
The churches of the Vall de Boí are an especially pure and consistent example of Romanesque art in a virtually untouched rural setting. The group of churches is a remarkable example of an important constructional style in human history, like that of Romanesque art, to which it contributes characteristics that are appropriate to both its religious and its secular aspects. The Vall de Boí illustrates the continuous occupation of an area of land. The churches that were built in the Middle Ages at the instigation of a single family symbolize the affirmation and geographical settlement at the time historical Catalonia was created.
The Vall de Boí is screened by the high peaks of the Beciberri/Punta Alta massif, in the high Pyrenees. Its scenery is one of woodland and meadows, adjoining and surrounding the small villages. The Arab invasion of the Iberian Peninsula never penetrated the valleys, but they were exposed around the beginning of the 2nd millennium to cultural influences, brought there by merchants, by itinerant monks and by Christian pilgrims travelling to Jerusalem and Santiago de Compostela. In the 11th century new cultural styles were brought into Catalonia from Italy, particularly Lombardy. This new cultural movement was late in reaching the remote Vall de Boí. The exceptional number of Romanesque churches in the valley is attributed to the fact that large quantities of silver came into the region.
The Vall de Boi isn’t hard to get to but you do have to go out of your way to get there. This site is a collection of 10 12-13th Century churches which reside in the small villages of the Vall de Boi. The churches, like many in the Catalonian region, are of a Romanesque design. In fact I saw many churches throughout the Catalonian Pyreneese which were very similar in style and age to the churches found in the Vall de Boi. Beyond their architecture, what makes many of the churches special are the frescos which can be found inside. Most of the frescos have undergone or are undergoing renovation. If you visit the Vall de Boi, take the time to visit Aigüestortes i Estany de Sant Maurici National Park. It is a beautiful Pyrenees park easy driving distance from the Churches.
View my complete list of UNESCO World Heritage Sites.