English: Rummu Quarry Lake is known for its crystal clear water (due to which the lake has earned the nickname "Light Blue Lagoon") & its interesting history. The quarry behind Murru prison was once completely dry. Limestone was mined there through the ages. Prisoners in Murru prison were the main workers. The sinking of the quarry essentially began with the re-independence of the Republic of Estonia. There was no longer such a demand for crushed stone production, & due to the change in laws, the work of prisoners and also the entire work organization in the lime quarry were interrupted.