World Tourism Organization & United Nations Environment Programme. Terrestrial Ecosystems Branch. Industry and Environment Programme Activity Centre. (1992). Guidelines: Development of national parks and protected areas for tourism. IUCN.
Παραπομπή σε μορφή Chicago (17η εκδ.)World Tourism Organization και United Nations Environment Programme. Terrestrial Ecosystems Branch. Industry and Environment Programme Activity Centre. Guidelines: Development of National Parks and Protected Areas for Tourism. Madrid: IUCN, 1992.
Παραπομπή σε μορφή MLA (9th εκδ.)World Tourism Organization και United Nations Environment Programme. Terrestrial Ecosystems Branch. Industry and Environment Programme Activity Centre. Guidelines: Development of National Parks and Protected Areas for Tourism. IUCN, 1992.