It's hard to picture now, but the calm, forest-ringed water of Lake Geiseltal in Saxony-Anhalt used to be an open-cast lignite mine. Diggers worked the Geisel valley from the late 1600s until 1993, most recently under East German rule. When the pumps stopped, the enormous pit was allowed to flood, and about a decade later Germany had a new lake — roughly seven square miles of it, the largest artificial lake in the country.

Nature has done the rest. More than 240 bird species have been recorded around the shores, and the fish stock is healthy enough that anglers regularly pull out northern pike, European perch and Prussian carp. On summer days the water is full of sailboats, motorboats and swimmers, with sunbathers stretched out on the sand at Stöbnitz Beach.

The water is the main draw. From May to September you can rent everything from SUPs and kayaks to motorboats and luxury pontoons at Mücheln Marina on the southwest corner — no boating licence required. The lake is big but simple to navigate, and parts of it plunge to around 250 feet, with visibility good enough to make it a serious freshwater diving spot. Submerged forests and old manmade structures are still down there. Two official dive bases, one near Mücheln and one on the eastern shore, rent gear and run instruction; divers must register with one of them before going under.

If you'd rather stay dry, a 15.5-mile trail loops the entire shoreline, walkable year-round and bike-friendly — rentals at the marina. Three observation towers, each about 46 feet tall, break up the walk, and the Weinbau am Geiseltalsee vineyard on the north shore pours local wine in its bar from late March to October.

Leipzig is the nearest big city, about an hour by car and an easy day trip. By public transport it takes roughly twice as long, with a train-to-bus transfer in Halle. Mücheln, a town of about 8,000, is the practical hub with pubs, restaurants and a handsome stone town hall around its central square. Accommodation is mostly pensions and guesthouses in Mücheln and Braunsbedra on the south side, plus campgrounds along the water — Geiseltalsee Camp sits right beside Stöbnitz Beach and the dive centre, open roughly May to September, with tent pitches as well as RV spots.

For travellers worn out by Germany's busier hotspots, this is a low-key alternative: a swimmable, diveable, cyclable lake with an honest industrial backstory, an hour from an underrated city, and rarely crowded.