Why Mayener Grubenfeld stands out
The Mayener Grubenfeld is best known for the extraordinary continuity of its basalt mining, from Neolithic grain-grinding stones through Roman querns exported as far as Roman Britain and North Africa, up to industrial-era paving stone extraction in the 20th century. Its underground Geglöcks, vaulted chambers made from the natural bell-like columns of basalt, are among the most distinctive mining landscapes of the region. The site is also recognized as one of the most important bat hibernation and swarming sites in Central Europe. Frost-free, humid, and undisturbed, the disused galleries shelter around 14 bat species plus two further species observed hunting in the area; counts and estimates suggest roughly 50,000 to 100,000 bats use the caves seasonally, drawing animals from up to 300 kilometres around during the late-summer swarm period.
Mayener Grubenfeld history and protected-area timeline
Mining at the Mayener Grubenfeld has been documented, continuously and without major interruption, for roughly 7,000 years. Early Neolithic fragments of quern stones from the late fifth millennium BCE already show the rock being collected and shaped; by the Bronze Age urnfield era, around 1000 BCE, small formal quarry pits had been cut into the basalt, and by the Michelsberg culture, stone axes, hammer-stones, and rill-strike balls were also being made from the site. In the Iron Age, Hallstatt and La Tène craftspeople used the same basalt for more advanced quern stones, including the characteristic biconical Napoleon's-hat stones.
Roman control of the area, beginning in the mid-first century BCE following the Gallic Wars, transformed the field into an industrial millstone district. Around 600 workers are estimated to have been employed at the Roman peak, supplying hand-mills for legionaries, large horse- or man-driven mills known as Göpelmühlen, and rough building stone to markets across the Roman West. Millstones from Mayen have been identified by petrological analysis in Roman Britain, at sites along the upper Rhine and Danube, and as far away as Roman Volubilis in northern Morocco; the same trade continued into the Viking world via Haithabu.
From the late Middle Ages onwards, around 1400 CE, the work shifted heavily underground. Shafts roughly seven to eight metres in diameter were sunk through the tuff cover into the basalt below, where miners exploited the rock's columnar jointing to create vaulted Geglöcks chambers that were then extended laterally into cave-like galleries. From about 1700, human- and horse-powered Göpelwerke lifted stone out of these shafts.
In the second half of the 19th century, the advent of roller-mill technology in large industrial flour mills collapsed demand for traditional basalt millstones. Mayener millstones were largely replaced by imported French freshwater quartzite and the underground millstone workings were abandoned around 1870 and fully given up by about 1900. The galleries then survived primarily as brewery cellars, a use that several Mayen breweries maintained into the mid-20th century. Above ground, the focus moved back into open-cast stone quarrying, mechanised from the 1920s onwards, mechanised crushing for ballast and paving. A railway line opened in 1878 between Andernach, Mendig, and Mayen mainly to carry basalt. After the workable reserves were exhausted, the last operations within the historic field closed in the 1970s, although basalt is still commercially quarried along its northern and eastern edges today.
Mayener Grubenfeld landscape and geographic character
The Mayener Grubenfeld sits in a gently undulating section of the Vulkaneifel, its surface shaped both by the underlying Quaternary volcanic geology and by 7,000 years of human extraction. The shallow-tilled, altered older bedrock here belongs to Devonian clay and slate, onto which the lava of the Bellerberg volcano, dating from roughly 140,000 to 200,000 years ago, poured in three broad flows running some 2.5 kilometres long and averaging 1.2 kilometres wide down to the Nette valley. With cooling, the lava hardened into a roughly 10 to 30 metre thick basalt sheet, whose porosity of up to 25 percent volume came from gas bubbles trapped in the slowly degassing magma.
Later volcanic activity blanketed the basalt with an additional covering up to ten metres thick of breccia-like Dielsteiner Gebirge, a coarse mix of trass tuff, pumice, slag, and other volcanic debris. Across the millennia, erosion stripped parts of this cover away, locally exposing the basalt at the surface, which both enabled early quarrying and shaped today's varied surface topography: low plateaus and spoil heaps punctuated by circular shaft openings, weathered quarry faces, and steep rims where basalt columnar jointing is visible.
Where the surface has been left without further disturbance, the land has returned to a mosaic of dry grassland, ruderal vegetation, overgrown scree slopes, scattered trees, and patches of damp ground around flooded pits. The largest water-filled former quarry, the Silbersee, anchors the visual rhythm of the preserved area. Around it, the remaining shafts, intact Geglöcks, abandoned crane bases, narrow-gauge trackways, the settling basin, and the partly ruined processing buildings together give the landscape an unusually layered industrial-archaeological character.
Mayener Grubenfeld ecosystems, habitats, and plant life
Nature has reclaimed the formerly active Mayener Grubenfeld in decades of quiet regrowth, producing a mosaic of habitats unusual for the region. The dry, sunny, stony slopes and ledges support species-rich, semi-dry grassland and ruderal communities; frost-free, humid basalt caves provide subterranean conditions rare under open skies; and the water-filled quarry hollows recreate pond-like micro-habitats otherwise missing from the surrounding agricultural and forested Eifel landscape.
On the surface, the quarry edges and stone-strewn ground create dry grasslands similar in character to the volcanic outcrops elsewhere in the Vulkaneifel: warm, exposed, and botanically distinctive. Around the water-filled hollows and damp cave mouths, conditions shift to moisture-loving communities of rushes and reeds, while fallen basalt blocks and rubble piles provide microhabitats for ground-nesting insects, reptiles, and small mammals.
The combination of dry, sun-exposed basalt, cool humid caves, and standing water on the same compact site has allowed a wide range of plant communities to coexist. The very different microclimates enable thermophilic species to live door-to-door with cave-dwelling fauna, and the area is now an important refuge within an otherwise fairly intensively used regional landscape.
Mayener Grubenfeld wildlife and species highlights
Bats define the wildlife identity of the Mayener Grubenfeld. At least 14 bat species hibernate in the cool, frost-free galleries of the former basalt mine, and two additional species have been recorded hunting or as skeletal remains. Documented hibernators include the barbastelle, northern bat, Bechstein's bat, Daubenton's bat, the pond bat, Natterer's bat, the whiskered bat, Nathusius's pipistrelle, the common pipistrelle, Brandt's bat, the whiskered bat's close relative Myotis mystacinus, the greater mouse-eared bat, the greater horseshoe bat, the brown long-eared bat, and the grey long-eared bat. The lesser horseshoe bat, lost from the region by about 1960, very likely once lived in the site as well. Several of these species appear on Germany's red list of threatened fauna.
The overwintering bat population is estimated at 50,000 to 100,000 individuals, and during the late summer and autumn swarm period bats arrive from as far as 300 kilometres around. Together with the caves at Niedermendig, the Mayener Grubenfeld is regarded as probably the most important bat hibernation site in Germany and one of the most significant in Central Europe according to EUROBATS.
Beyond bats, the field supports unusually rich cave fauna. A cave-cricket species discovered here in 1999 is otherwise almost unknown in Germany, and the cave-dwelling harvestman Leiobunum religiosum, normally a species of the Alps and the Mediterranean, also lives here. Reptiles including the western green lizard, the wall lizard, the sand lizard, the slow-worm, the grass snake, and the smooth snake share the dry quarry edges with amphibians such as the common toad, the natterjack toad, and the midwife toad. Dry grassland preserves species-rich insect communities including butterflies such as the scarce Spanish flag moth, grasshoppers, and wild bees; insect hotels were installed specifically to support these groups. The quarry faces also provide breeding sites for rare birds such as the woodlark and the common whitethroat, while eagle owls have been documented breeding in the basalt cliffs.
Mayener Grubenfeld conservation status and protection priorities
Ecologically, the Mayener Grubenfeld's most distinctive value lies in its underground microclimate. The frost-free, humid, dark basalt galleries, abandoned by industry, now provide some of the most valuable bat hibernation conditions anywhere in Central Europe, a function that depends critically on the voids being kept open, structurally stable, and undisturbed.
This value was formally recognized only in stages. Beginning in the 1990s, conservationists led by NABU Rheinland-Pfalz and supported financially by the Bundesamt für Naturschutz and the state of Rhineland-Palatinate began purchasing core galleries, including the MAYKO-Bierkeller, the Mauerstollen, and a third major gallery, and stabilizing them between 2009 and 2011 against collapse so that they could continue to serve as bat habitat. In 2000, parts of the site became part of the FFH area 'Unterirdische stillgelegte Basaltgruben Mayen und Niedermendig' (DE-5609-301), and on 2 May 2014, the larger Mayener Grubenfeld was officially designated as a Naturschutzgebiet under German law.
The conservation challenge at Mayen has been unusually layered. The site is at once a Natura 2000 habitat, a German Naturschutzgebiet, a protected cultural monument, an archaeological artefact, and a tourism destination. The site is also a station of the Vulkanpark in the Landkreis Mayen-Koblenz and falls within the Nationaler Geopark Laacher See, integrating the bat-protection work with industrial-archaeological presentation through the Erlebniswelten Grubenfeld visitor centre and the basalt sculpture park Lapidea.
Mayener Grubenfeld cultural meaning and human context
The Mayener Grubenfeld sits in a region whose identity is shaped by Quaternary volcanism and the long human use of its rocks. Centuries of trade moved Mayener basalt far from the Eifel: Roman millstones reached Britain and the Mediterranean world, including Volubilis in modern North Africa, and the same material appears in Viking-Age Haithabu. The local brewing tradition that grew up around the underground cellars after Roman and medieval mining is still a recognizable part of the regional culture, and the tradition of the tri-annual Lapidea stone-sculpture symposium between 1985 and 2006 tied the modern identity of the site directly back to its geological resource.
Until the early 2010s, the landscape was also an active industrial zone, with newly planted forestry, agricultural fields, and an industrial estate sitting above older shafts that were largely filled or demolished. The shift toward treating the same terrain simultaneously as a habitat for rare bats, a monument to 7,000 years of basalt mining, a Natura 2000 site, and an outdoor classroom within the Vulkanpark is itself an expression of the broader change in how Vulkaneifel landscapes are now valued, as a fusion of natural, cultural, and industrial heritage.
Top sights and standout views in Mayener Grubenfeld
The Mayener Grubenfeld combines three layers of value in a single landscape. First, a continuous 7,000-year mining record, traceable from Neolithic quern stones through Roman exported millstones to 20th-century railway ballast, anchored by the distinctive underground Geglöcks chambers made from the natural columnar jointing of the basalt. Second, an exceptional bat hibernation and swarming complex, with an estimated 50,000 to 100,000 bats across at least 14 species, drawing animals from up to 300 kilometres around in late summer. Third, a living cultural-landscape presentation, anchored by the Erlebniswelten Grubenfeld visitor centre at the edge of the field and by the Lapidea open-air basalt sculpture park.
Best time to visit Mayener Grubenfeld
Spring and early summer typically offer the mildest weather for walking the open terrain and viewing the protected surface flora and fauna, when the dry-grassland vegetation is most active and reptile and insect life are out. Late summer and early autumn are also visually distinctive but are also the bat swarming season, when bat conservation sensitivities restrict access to active galleries and require visitors to stay with guided offers. The underground galleries themselves maintain a fairly steady cool temperature year round, so visits are not strongly seasonal in the caves themselves. Bat observers, photographers of the Lapidea sculptures, and visitors interested in industrial-archaeological remains like the Silbersee and the surviving shaft openings will generally find the most informative conditions in the warmer months, when the surface paths are most pleasant and the contrast between the dry quarry edges and the small lakes is at its sharpest.
