‘This was once one of the dirtiest areas in East Germany,” says Sören, my tour guide from IBA Tours, as our bikes swoosh through the Lusatian Lake District. “When I was growing up here, before the Wall fell, we never hung our laundry outside, and we never wore white socks, because we knew they wouldn’t be white after a few minutes. The coal dust was everywhere, all the time.”

It’s difficult to connect this information with the pristine landscape around us, all soaring pine forests, glistening lakes and immaculate asphalt cycle paths. The only other major signs of life have been a smattering of fellow cyclists and a sedge of cranes in a field. We haven’t heard, let alone seen, a motorised vehicle – and there’s certainly no coal dust in the air now.

Aerial view of the Lusatian Lakeland. Photograph: Alamy

The development of this region is one of the former GDR’s biggest success stories, transforming what was once one of its primary lignite-producing areas into the largest artificial lakeland in Europe, stretching 50 miles across the states of Saxony and Brandenburg. The popular Spreewald area is just to the north, the Polish and Czech borders are around 55 miles away – as is the handsome city of Dresden – and Berlin can be reached by train in an hour and a half. It’s intriguing to think that each of the 26 lakes that make up this region was once an opencast mine. The mining continued throughout the 20th century, reaching peak production under the GDR regime, which was highly dependant on lignite as a natural energy resource, especially following the 1970s oil crisis.

The idea of turning mines into recreational lakes actually began in the GDR, when one of the mines near Senftenberg was flooded in 1973, on the recommendation of landscape planner Otto Rindt. Lake Senftenberg – nicknamed “Dresden’s Bathtub” – subsequently became the blueprint for the current development. Following reunification, the remaining mines were either taken over and cleaned up by Swedish company Vattenfall, or handed over to the federally owned LMBV (founded in 1994) for transformation into recreational areas.

Upper Lusatian heath and pond area in Saxony. Photograph: Alamy

Around 13 lakes are already accessible, with the rest a year or two away from completion, at a total cost so far of around €2.2bn. There are cycling paths encircling each lake, many of which criss-cross to create a 300-mile network. The central group either have been, or soon will be, connected by waterways, and associated infrastructures are being individually developed in an attempt to create a variety of experiences.

Some lakes have been left relatively undeveloped, while others, like the more eastern Spreetaler See, has been earmarked for boisterous watersports. The most developed lakes – Senftenberger and Geierswalder, connected by a €50m canal – are mostly geared towards families. Here you can find beaches, cafes and restaurants, and activities ranging from fishing and horse riding to quad-biking and diving. Accommodation ranges from campsites to floating rental apartments and the four-star Seeschlösschen Ayurveda Spa & Hotel.

Volleyball on Senftenberger lake beach. Photograph: Alamy

According to Kathrin Winkler, manager of Lusatian Lakeland Tourism, visits to the area have been increasing 10% annually. In 2015, there were around 300,000 overnight stays on Lake Senftenberg alone, with another 200,000 spread around the rest of the lakes. Most of the tourists hail from Saxony, Brandenburg and the Czech Republic, illustrating how the region has managed to remain something of a local secret.

The lakeland also carries huge symbolic value in terms of the country’s Energiewende, part of Angela Merkel’s renewable energy act, under which all nuclear power stations are to be closed by 2022 in an ambitious push towards clean energy. However, with lignite (together with stone coal) still providing 41.9% of national power, several mines are still in operation around the country, including three in the Lake District.

Cyclists at Großräschener lake.

After completing our 11-mile ride around Geierswalder lake, Sören brings me to a not-quite-finished one at Grossrächener, where his offices occupy the former buildings of the IBA-See – a federal and EU-funded project that, between 2000 and 2010, gave a huge boost to the area with around 30 creative projects. Some, like a floating discovery centre, are still awaiting completion, but finished sites such as the visitor centres in former mines and power stations, a water sports centre in Sedlitz and the ‘Rusty Nail’– a rust-coloured architectural tower with stellar views over the area – are now connected via the Lusatian Route of Industrial Heritage.

The former IBA offices, now known as the IBA-Terrassen, include a fairly slick cafe-restaurant that’s fronted by an attractive vineyard sloping down towards the lake. The adjacent marina is still in progress but the adjacent Seehotel Großräschen is already up and running. Originally built in the 1920s for Polish mine workers, it’s now a swish four-star with an intriguing museum of counterfeit artwork made by the Russian Posin brothers.

As we pass replicas of paintings, including a Mona Lisa, Sören remarks: “They are perfect for the area, aren’t they?” I look at him, nonplussed. “They’re artificial, too,” he smiles.

• The trip was provided by Brandenburg Tourism and Germany Travel. Accommodation was provided by Seehotel Großräschen (seehotel-grossraeschen.de), doubles from €109 B&B. For further information on the area, visit lausitzerseenland.de