Bancheva-Preslavska, Hristina, and Jochen Dallmer. “Alternative Urban Eco Tours for Responsible Consumption and Sustainability – the Example of Bulgaria”. European Journal of Sustainable Development 9, no. 3 (October 1, 2020): 416. Accessed May 6, 2021. https://ecsdev.org/ojs/index.php/ejsd/article/view/1093.