The quarry was originally established in the 1930s to provide labor for inmates from the adjacent Murru Prison.
The water levels rose so quickly after the pumps were turned off that some heavy machinery remains exactly where it was left.
The water clarity often exceeds 5 meters, making it a primary destination for underwater photography and training in Estonia.
The high lime content in the water creates the vibrant, Caribbean-like turquoise color.
The surrounding 'Ash Mountain' is a man-made formation consisting of waste material from the limestone excavation process.
Rummu is an underwater prison complex and limestone quarry located in Estonia, known for its partially submerged ruins and turquoise, highly transparent water. The site was once the location of the Murru Prison, where inmates performed limestone extraction until the site was abandoned following the collapse of the Soviet Union. When the pumping systems in the quarry were deactivated in the 1990s, groundwater levels rose rapidly, flooding the prison buildings and surrounding machinery. The resulting artificial lake features remnants of barbed wire fences, prison walls, and former equipment visible beneath the surface. Today, the site functions as a recreational area popular for swimming, diving, and stand-up paddleboarding. The distinctive blue hue of the water is a result of the limestone substrate and the depth of the flooded quarry. The area is surrounded by a large slag heap known as 'Ash Mountain,' which offers elevated views of the submerged ruins.
The summit of the Ash Mountain provides a panoramic view of the submerged prison ruins and the flooded quarry.
Bring water shoes, as the bottom of the lake is rocky and littered with submerged debris from the old prison structures.
Check water safety warnings before entering, as the submerged structures can pose entanglement hazards.
Visit on a weekday to avoid the significantly higher crowds that gather during sunny summer weekends.
Do not attempt to dive or snorkel alone or without checking the structural integrity of the underwater area you plan to enter.
Open for public access only during the summer season; closed during autumn, winter, and early spring.
No diving or swimming in areas marked as restricted; do not remove or disturb any industrial artifacts.
