Shaw, Trevor R., and Alenka Čuk. “The Underground Post Offices of Postojnska Jama, Slovenia, 1899 - 1945”. Acta Carsologica 32, no. 1 (May 23, 2016). Accessed May 3, 2024. https://ojs.zrc-sazu.si/carsologica/article/view/374.