In 1975, an ordinary high school in Phnom Penh was seized by Pol Pot's security forces and transformed into Security Prison 21 (S-21), the Khmer Rouge's most notorious detention and torture centre. Today, the site stands as the Tuol Sleng Genocide Museum, preserving the memory of the thousands who passed through its gates and never returned. Through photographs of former classrooms turned prison cells and the traces left behind, this project explores memory, loss and the lasting scars of one of Cambodia's darkest chapters. It examines how a place once filled with learning became a symbol of unimaginable suffering, and how Cambodia continues to reckon with its past nearly half a century later.