Between 1978 and 1981, Sophie Calle went on a clandestine exploration of the then abandoned Hôtel du Palais d'Orsay. She selected room 501 as her home and without any pre-established method, set about photographing the abandoned hotel over 5 years. As she explored, she picked up items she found: room numbers, customer reception cards, old telephones, diaries, messages addressed to a certain "Oddo" and more besides. What happened to room 501? More than 40 years later it has disappeared and an elevator has taken its place. At the invitation of Donatien Grau, the Musée d'Orsay curator, Sophie Calle returned, equipped with a flashlight, to explore the site again during the lockdown period. She hunted down the ghosts of the Palais d'Orsay, now connected to the present by the visitors that had also deserted the museum. The work reconstructs the artist's archive of photography, letters, invoices and other daily items which bring a forgotten past back to life. To provide commentary on her discoveries, Sophie Calle called upon the archaeologist Jean-Paul Demoule, who writes a series of texts combining fact and fiction. All this evidence has been assembled together to create an objet d'art which resembles an investigation notebook.