All asylum seekers who arrive in Australia's territorial waters by boat are subject to mandatory, indefinite and unreviewable detention on Nauru and Papua New Guinea. This offshore detention regime is characterised by a high degree of secrecy, low levels of transparency and accountability, and few opportunities for external oversight. This has created a closed, controlled environment, in which people are routinely neglected and harmed. To better understand the human impact of Australia’s offshore detention regime, this article draws on research from social psychology regarding human behaviour in closed institutions. This research – which has substantially informed prison policies throughout the Western world – demonstrates the critical importance of external oversight, openness and transparency for the protection of human rights of people in closed institutions. This knowledge has not been applied to Australia's offshore immigration detention regime. To the contrary: creating a closed, opaque system of detention has been an explicit policy goal of the Australian government. By actively restricting transparency, this research demonstrates that not only are the abuses of detainees' human rights hidden from the public eye, they are inevitable.