The Museum's Long-term Exhibition presents visitors with a general characterization of the Portuguese dictatorial regime (1926-1974), its means of oppression on the population (through censorship and the repressive action of police and political courts), the means of response by oppositions, semi-legal and clandestine, as well as aspects of the anti-colonial struggle that led the military to overthrow the regime by military coup, in 1974. On floor -1, visitors can still see part of the structures of the building where the Museum is housed and an archaeological show raised from its subsoil.