The 'trass' extracted here was traditionally mixed with lime to create a water-resistant mortar, used extensively in major canal and harbor constructions.
The Laacher See eruption, the source of the trass material, was the most powerful volcanic event in the Eifel region during the Holocene epoch.
The caves are considered an important overwintering habitat for several protected species of bats.
The mining of trass in the Brohl Valley dates back to Roman times, though the specific caverns seen today were significantly expanded during the 19th century.
The rock layers inside the caves contain visible fragments of pumice and other volcanic ejecta, providing a cross-section of geological strata.
The Trasshöhlen are a series of man-made caves carved into layers of volcanic trass, a solidified ash deposit from the Laacher See volcano eruption approximately 13,000 years ago. Historically, these tunnels were excavated by miners to extract the trass, which was a highly valued additive for hydraulic mortar used in concrete production. The caves are part of a larger geological network within the Brohltal valley. The interior environment remains cool year-round, characterized by porous, pale volcanic rock walls. Visitors can explore the cavernous chambers via a designated trail system. The site highlights the region's intense volcanic history and the industrial mining heritage of the Eifel mountains. The caves are integrated into the local hiking infrastructure, including segments of the Traumpfad trails.
The entrance to the main cave gallery, where the interplay of light on the textured, pale volcanic rock is most distinct.
Bring a flashlight, as some deeper sections of the cave system can be dark.
Wear sturdy, closed-toe footwear with good grip, as the ground can be uneven or damp.
Combine your visit with a hike along the Brohltal trails for a more comprehensive view of the volcanic landscape.
Do not enter sections marked as cordoned off or restricted for safety or conservation reasons.
The caves are generally accessible year-round, but specific sections may be closed periodically for bat conservation during winter months.
Do not touch the cave walls to preserve the geological surface and avoid disturbing hibernating bats.
