From the mid-1800s to 1970, this lake served as one of Denmark’s largest granite mines, shipping granite to various locations across the country from the nearby harbor. Following its abandonment, water accumulated, giving rise to one of Denmark’s most recognizable lakes. Featuring crystal-blue waters and surrounded by the scenic hill of Hammeren, it stands out as one of Denmark’s finest unnatural wonders.

With a surface height of approximately seven meters, this former granite mine has become a premier location for cliff diving in Denmark. Every year, thousands of visitors plunge into its waters or embark on a hike to the stunning vantage point atop Hammeren.

From the summit of Hammeren, another, albeit smaller, lake named Krystalsøen (Crystal Lake) unfolds. It is at this location that you can experience Denmark’s longest zipline, stretching 260 meters with speeds reaching up to 70 kilometers per hour, culminating in a thrilling splashdown in the Opal Lake 50 meters below. If the daring adventure isn’t your preference, you can simply revel in the panoramic view of Northern Bornholm.