The Rummu quarry, located near the village of the same name in the former Vasalemma Parish in the Harju County, northern Estonia, is justly considered one of the most unusual and picturesque sights of the country. Today it has turned into a magnificent azure lake, which locals and travelers often call the blue lagoon. To see this natural and manmade wonder, from Tallinn, go straight along the Vasalemma highway to the Rummu village. The journey will take you about an hour. Abandoned prison buildings will serve you as a waymark.

The former local prison, known as Murru, was founded in the 1940s when Estonia was part of the Soviet Union. It was a correctional facility where four hundred prisoners served their prison terms of penal servitude at the Rummu limestone quarry. They pumped out groundwater, which was afterward used in nearby towns and farms.

When in 1991 the Soviet Union collapsed and the demand for mining sharply decreased, the Estonian government shut down the Murru prison, and the nearby quarry was abandoned. Soon, most of this area, with its many buildings and amenities, went underwater and turned into a picturesque azure lake, which has become a local landmark.

Today, the Rummu quarry has become a Mecca for water sports enthusiasts. Locals and travelers wish to see and explore this unique place with the underwater prison ruins, a sunken elfin forest, and an ash limestone hill. One of the most popular and affordable ways to do this is by scuba diving to the lake bed.

The limpid blue lake in the Rummu quarry possesses stunning water clarity and a unique bed, covered with a true underwater museum of the former prison buildings. During the dive, you will see several buildings surrounded by majestic walls, drowned machinery and equipment. Besides, there is a submerged forest at the bottom of the quarry that creates a mystical underwater landscape and an unparalleled mood.