The workers discovered the trash bag after they opened a small, rusted metal door that revealed a cavity that had been hidden by more than 30cm of ivy, gallery employee Dario Gallinari told CNN in December.
The portrait, which depicts a young woman with rouged cheeks and dark hair, disappeared from the gallery during a building renovation in 1997 and was presumed stolen.
The painting’s disappearance in 1997 was somewhat of a mystery — its frame was found near the gallery’s skylight shortly after the work disappeared, leading to speculation that the thieves could have entered and left through it.
A forgery of the painting, wrapped up and posted to a disgraced politician, was seized by authorities a month later, Reuters news agency reported — adding further intrigue to the case.
According to head of culture Jonathan Papamarenghi, “Portrait of a Lady” was second on the list of the most valuable artworks missing in Italy, after a work by Caravaggio stolen from a church in Sicily in 1969, Reuters reported.
The painting was part of a series of female portraits that Klimt painted in the last few years of his life, some of which were never finished.
Piacenza is a northern Italian city of about 100,000 and is about 69 kilometers (43 miles) southeast of Milan.