In 1938, the Rummu Prison was founded at a limestone quarry in Rummu, Estonia.
Inmates at this prison camp were forced to mine limestone alongside prisoners from the Murru Soviet Prison until 1991, when the Soviet Union collapsed and Estonia regained its independence. The place was abandoned soon after, and because no one was pumping groundwater out of the quarry anymore, the ruins eventually became submerged in a new lake.
Parts of the prison can still be seen today, but some of the buildings and mining machines are completely underwater. And even though the lake bed is peppered with pieces of thick concrete, tree branches, rebar spikes, and barbed wire, people can’t help but plunge right in and explore the area.