or it may be set in a walled close as at Canterbury. There may be a number of associated monastic or clergy buildings, a bishop's palace and often a school to educate the choristers. Artworks, treasures and tourism Many cathedral buildings are very famous for their architecture and have local and national significance, both artistically and historically. Many are listed among the UNESCO World Heritage Sites. Many cathedrals, because of their large size and the fact that they often have towers, spires or domes, have until the 20th century, been the major landmarks in cities or in views across the countryside. With highrise building, civil action has been taken in some cases, such as Cologne Cathedral to prevent the vista of the cathedral from being spoiled. Because many cathedrals took centuries to build and decorate, they constitute a major artistic investment for the city in which they stand. Not only may the building itself be architecturally significant, but the church often houses treasures such as stained glass, stone and wood statues, historic tombs, richly carved furniture and objects of both artistic and religious significance such as reliquaries. Moreover, the cathedral often plays a major role in telling the story of the town, through its plaques, inscriptions, tombs, stained glass and paintings. For these reasons, tourists have travelled to cathedrals for hundreds of years. Many cathedrals cater for tourists by charging a fee to any visitors outside service times or requesting a donation or making a charge to take photos. Cathedrals that are particularly popular tourist venues sometimes provide guides, leaflets, souvenirs and cafes. See also Architecture of cathedrals and great churches Architecture of the medieval cathedrals of England Basilica Cathedral architects in England. Cathedral diagram Duomo Gothic cathedrals and churches French Gothic architecture English Gothic architecture List of basilicas List of cathedrals List of highest church naves List of largest church buildings in the world List of regional characteristics of European cathedral architecture List of tallest churches in the world References Further reading Carl F. Barnes, Jr. "Cathedral". In: Joseph Strayer, ed. Dictionary of the Middle Ages. New York: Scribner's, 1938. Vol. III. pp. 191–92. Johnson, Paul. British Cathedrals. London: Weidenfeld & Nicolson, 1980. . Richard Utz. "The Medieval Cathedral: From Spiritual Site to National Super-Signifier". The Year's Work in Medievalism 15 (2001), 127–31. Richard Utz. "The Cathedral as Time Machine: Art, Architecture, and Religion." In: The Idea of the