The Vogelsberg (Birds Mountain) is the largest vocanic area in middle Europe and geological very interesting. But volcanic rocks are not soluble, in order to have caves, and volcanic caves (lava tubes) are also not known in this area.
The Vogelsberg is located in a sandstone belt, extending from the Pfälzer Wald across Odenwald, Spessart, Kassel to the Solling. This rocks are also no good for caves.
So the small area of limestones from the upper Triassic around Steinau is an extraordinary exception. This area is karstified, and although the caves are rather small, there is a single show cave in this area.