Situated in the access road above the Presidential Palace in Carthage the restored complex of the Kobba is prohibited for visitors. In historic times the building had been constructed beneath the horizontal level of its surroundings, so that it was somehow hidden to the public eye. The intention of being hidden was attributed to the user’s assignment to a religious community, for whom it was a sanctuary. The access leads to different underground rooms by a staircase with a tunnel vault. The rooms show a rich variety of different vault constructions. According to the different room sizes and functions, the arrangement of its vault shapes is executed as tunnel vaults as well as domes meshed in different combinations of smaller and bigger cupolas. The vaults were constructed with lost formwork from small earthenware pipes which allow a wide variety of dome forms. The formwork was covered with Roman concrete, called Caementitium, which had similar stable characteristics as modern concrete. The traces of some earthenware pipes are still to be seen. A system of roof lights provides fresh air and some daylight.