Opal Lake (Opalsøen), Bornholm

Granite Quarry Turned Emerald Basin

Opal Lake sits in the scar of Hammerbruddet, once one of Bornholm’s most important granite quarries. From the late 19th century until 1970, stone was cut from these walls and shipped across Denmark, fuelling a boom that shaped the island’s economy and coastline. When extraction stopped, groundwater and rain slowly filled the pit, transforming an industrial void into a deep, enclosed lake with remarkably clear, mineral-rich water. Today the old workings are softened by nature. Steep rock faces plunge straight into the lake, their grey and rust-red tones mirrored in glassy green-blue water that hints at the site’s opalescent name. The geometry of blasted quarry terraces is still visible, but moss, heather and scrub now cling to ledges, while seabirds patrol the cliffs and calls echo around the basin.

Cliffs, Colors and Raw Coastal Drama

Opal Lake lies just inland from Bornholm’s northernmost headland, wrapped into the granite dome of Hammeren. The setting is surprisingly compact yet dramatic: sheer walls up to several metres high, broken boulders at the waterline, and a tight bowl of rock that can feel almost amphitheatrical on still days. Sunlight plays a starring role here, turning the water from dark bottle-green to bright turquoise as the angle of light shifts. A short climb onto the surrounding knoll of Hammerknuden opens the scene wider. From here you can look down into the quarry bowl and, beyond it, pick out Hammersøen (Bornholm’s largest natural lake) and the open Baltic Sea. On clear days, the ruins of Hammershus castle silhouette the horizon, connecting Opal Lake’s modern industrial past with the island’s medieval story.

Swimming, Cliff Jumps and a Zipline Splashdown

For many visitors the main draw is getting into – or above – the water. The lake is very deep and drops off quickly from the shoreline, making it suitable only for confident swimmers, but rewarding them with cool, sheltered water even on breezy days. In summer, braver souls leap from designated cliff ledges around seven metres high, using the quarry walls as natural diving platforms. When operating in the high season, a long zipline stretches from the higher ground above the lake, sending harnessed riders flying out over the water before a final splashy landing. The quarry walls also offer opportunities for supervised climbing and abseiling with local operators. Away from these adrenaline spots, quieter banks and rocky outcrops provide space to sit, dangle your feet and enjoy the reflections.

Trails Through Hammerknuden’s Rough Nature

The lake is threaded into a wider network of paths around Hammerknuden, a protected landscape of rocky heath, low pines and coastal viewpoints. Simple tracks loop the water’s edge in about a quarter of an hour, with side paths branching up to viewpoints or across to neighbouring Hammersøen. Underfoot, expect a mixture of gravel, exposed rock and occasionally uneven sections where old quarry infrastructure once stood. Goats are sometimes used for grazing on the slopes, adding a slightly pastoral touch to the otherwise stark scenery. Birdlife finds niches on ledges and in crevices, and the absence of major buildings nearby keeps the soundscape mostly to wind, voices and the occasional splash. It is easy to combine a circuit of the lake with a longer ramble across Hammeren’s headland.

Seasons, Light and Practical Atmosphere

Opal Lake is accessible year-round, but its character shifts with the season. In summer it can feel lively and adventurous, with swimmers, zipline riders and families exploring the rocks. Spring and autumn bring a quieter, more contemplative mood, with cooler water but often crisp visibility and dramatic skies over the Baltic. In winter, when conditions allow, the quarry walls and still surface take on a stark, almost monochrome beauty, though bathing and exposed paths demand extra caution. Facilities around the site remain minimal, preserving a raw feel. Simple information boards help explain the quarry history and outline walking routes. Nearby parking areas and basic amenities serve as a base before you step into the more elemental world of rock, water and sky that defines Opal Lake.