‘EIG’ gave a free short theoretical and practical course on the electrical tomography technique to teachers from the University of Engineering and Architecture (in Spanish, Escuela Superior de Ingeniería y Arquitectura) of the National Polytechnic Institute (in Spanish, Instituto Politécnico Nacional). For the practical part of the course we chose to carry out a campaign in an area known for the existence of cavities, in which we could confirm the field data acquired and processed with the structures (cavities) of relatively easy access.