Besucherbergwerk Kleinenbremen – Blaue Lagune
A former iron-ore mine (Grube Wohlverwahrt) at Kleinenbremen near Porta Westfalica, opened as a show mine in 1988. In its lower section groundwater flooded the workings after the pumps were switched off, forming the 'Blaue Lagune', an underground lake far inside the mountain. Divers reported very clear 7–8 °C water, a depth of about 20 m and a guideline; there is little life, just rock and sediment. Equipment was carried in by the mine railway.
Tiefe: 0–20 m