Buried beneath Frederiksberg Hill in the heart of Søndermarken Park, in Copenhagen, is a massive underground space that once held up to 16 million liters of water for the residents of Copenhagen. Before the Cistern was built, Copenhagen had some major water problems during the 1800s. Among other things, the water source was heavily polluted, and as the city grew vertically it became more and more difficult for water to reach the upper floors. When a cholera epidemic in 1853 claimed the life of more than 4,700 residents, a decision was made to build a new cistern to improve Copenhagen’s drinking water.

Frederiksberg Hill was chosen as the location for the new reservoir because of its height, and excavation began in 1856. The reservoir was completed three years later. Originally the reservoir was an open pool of water, but in 1889 it was covered with a molded concrete structure to minimize chances of pollution and infection.

A water, light and sound installation by artist Ingvar Cronhammar in the Cisternerne. Photo credit: unknown/imgur