Visit the Opal Lake at the Northern tip of Bornholm
From the 2nd half of the 19th century Bornholm witnessed a tremendous granite industry. Granite became one of the most important export goods of Bornholm. There was a real boom in the granite industry on the island and first in 1970 the quarry was closed.
You have several hiking trails running by the lake. And if you walk up on the top of the cliffs, you get a breathtaking view over the whole area and even the Baltic Sea and Hammershus castle ruin.
You can swim in the Opal Lake, but please note, that the lake is very deep – and therefore only suited for people, who can swim, as you won’t be able to stand on solid ground anywhere in the lake.