A few kilometers away from the Trass caves in the Brohltal lies Lake Laacher, a "former" volcano that, during an eruption 13,000 years ago, shot so many lava particles into the atmosphere in a gigantic column that, when it rained at the same time, they filled the surrounding valleys up to 60 meters high.

This lava and ash particles, which have caked together over time, are called trass in the region. The material was already mined by the Romans because, together with lime and water, it becomes a mortar that can be used, for example, to build houses.

The Burgbrohl Volcano & Panorama Trail leads directly through some of the large caves.