Some of the most avant-garde contemporary art in Copenhagen is quite literally underground.

Cisternerne is an old subterranean reservoir that supplied drinking water to all of Copenhagen from the 1850s until the 1930s, and also doubled as a reflection pool for the nearby Frederiksberg Castle. When the cisterns were finally drained and covered in 1981, they were used as an exhibition space for modern glass art for a decade before they were adopted into the Frederiksberg Museum.

Today, Cisternerne, which lies below the grounds of Søndermarken park, functions as a multimedia installation space. The only indication of its presence are the two towering glass pyramids that mark its entrance and exit points. When you descend into the dripstone cave (the only one of its kind in Denmark), the atmosphere changes drastically. The air is typically at 100 percent humidity, but the temperature is usually a cool 47˚F. Impressive stalactites and stalagmites extend from the floor and ceiling, but it’s the art people come to see in this unique setting.

The Frederiksberg Museum commissions an artist to create an exhibition for Cisternerne every year. The artists use the unusual cavern setting—along with its darkness, humidity, and reverberant acoustics—to create equally unusual art. The dark, dank series of tunnels prove to be an excellent, if sometimes creepy, backdrop for light and video installations. Past installations include a mossy replica of a Japanese shrine by Hiroshi Sambuichi.