P. S. Caetano, M. L. de A. S. Patuleia, and M. I. M. Ferreira, “ABOVE AND UNDER GROUND: A PROPOSAL FOR URBAN GEOTOURISTIC TOURS IN LISBON”, Tour Manage Stud, pp. 426–437, Jan. 2012, Accessed: Apr. 28, 2024. [Online]. Available: https://www.tmstudies.net/index.php/ectms/article/view/207