Żaba, J. and Gaidzik, K. “The Ngorongoro Crater as the biggest geotouristic attraction of the Gregory Rift (Northern Tanzania, Africa) – geotouristic valorization, touristic development and hazard”, Geotourism/Geoturystyka, (24-25), p. 47. doi: 10.7494/geotour.2011.24-25.47.