Kreidesee Hemmoor

An historic opencast chalk mine about 50 miles outside of Hamburg in northern Germany was later flooded by groundwater seeping up from below as the mine delved deeper and deeper. When mining ceased in the 1970s, the entire mine was eventually filled with fresh water. The factory buildings that surrounded the mine were demolished, and some of them were dropped into the lake to provide support for the pit's edges.

Hemmoor Kreidesee (Kreidesee means "chalk-lake" in German, referring to the lake's mining background) became a popular dive destination in the 2000s. To assist the diving, a number of artificial reefs have been created in the lake, and a dive center has sprung up near the lake's entrance.

This ex open cast chalk mine, which was flooded when mining ceased in the 1970s, is an intriguing quarry dive for all levels of experience. The remnants from the mining era are perhaps the most intriguing parts of this location. You may still see the flooded houses and woodland that were above water before the pumps stopped and the mine gradually filled with water if you swim down the old road that led to the mine.

If you're in North Germany, this is a must-see with a maximum depth of 60 meters and visibility of up to 30 meters.

• Location: Lower Saxony