Restoration work in the courtyard of Istanbul’s Hagia Sophia has revealed a vast and unexpectedly complex network of six underground structures. The discovery, exceeding initial expectations, suggests the presence of a previously unknown subterranean city beneath the historic landmark. Experts were surprised by the scale and intricacy of the underground network. The structures’ purpose and age are currently under investigation, though they are believed to be historically significant. Further excavation and analysis are planned to fully understand the scope and nature of this archaeological find. The discovery promises to offer new insights into the history of the Hagia Sophia and the surrounding area.