摘要:Visible trends in city tourism related to the development of sustainable tourism clearly imply an increase in the significance of green areas and the development of nature-based tourism. Natural areas in cities that ideally fit the assumptions of sustainable tourism are nature reserves—areas where protection of the valuable environment is a priority. This paper aims to highlight that nature reserves are green spots in cities that can be excellent sites for sustainable tourism. The choice of big cities was dictated by the fact that they have the highest requirement for recreational green spaces due to a high concentration of tourist traffic in historic city centres and a clearer need for sustainable forms of tourism. Sixteen nature reserves in five big Polish cities with a population of more than 100,000: Gdańsk, Łódź, Poznań, Toruń, and Warsaw were selected for the study. Field surveys were carried out in nature reserves to see whether basic tourism facilities providing information about nature, supporting education, and conservation of the natural environment existed in the publicly available areas of such reserves. The attractiveness of nature reserves to tourists and their suitability for developing sustainable tourism was evaluated through score-based valuation of the reserves. The valorisation index was used for a synthetic rating and classification of the reserves in terms of attractiveness. The results of surveys imply a possibility of using selected nature reserves in cities for developing sustainable forms of active tourism—in particular hiking and cycling, educational tourism and daily recreational activities of city residents. The sites in question can be regarded as attractive ecotourism products, and as such hold the potential to become a popular destination among tourists and eco-tourists in particular.