Pyrite Lake and Emerald Lake are two former clay pits located close to the coast near Sorthat-Muleby on western Bornholm. The lakes were formed when clay and coal extraction for the Hasle clinker and firebrick factory ceased, and the water-filled pits now appear as deep lakes surrounded by forest and hilly terrain within Hasle Lystskov/Hasle Klinker Forest. The area is known for its hiking trails, proximity to the sea, and traces of the old industry, and is used today for nature experiences, swimming in certain spots, and recreational fishing.
