Quantum correlations are at the heart of quantum information science1–3. Their detection usually requires access to all the correlated subsystems4,5. However, in many realistic scenarios this is not feasible, as only some of the subsystems can be controlled and measured. Such cases can be treated as open quantum systems interacting with an inaccessible environment6. Initial system–environment correlations play a fundamental role for the dynamics of open quantum systems6–9. Following a recent proposal10,11, we exploit the impact of the correlations on the open-system dynamics to detect system–environment quantum correlations without accessing the environment.We use two degrees of freedom of a trapped ion to model an open system and its environment. The present method does not require any assumptions about the environment, the interaction or the initial state, and therefore provides a versatile tool for the study of quantum systems.