Rummu quarry was used as a mining site for Vasalemma marble (a kind of limestone) for a very long time. Most of the workforce came from among the detainees of Murru prison. When the prison was closed, pumps that kept the quarry and the prison dry were shut down. The water rose so quickly that it flooded the large mining excavator, buildings, and other equipment. Now, these make up for a unique underwater museum which can be seen thanks to the extremely transparent water, making it a perfect destination for divers.