The Vogelsberg is an old volcanic region with the largest basalt mass in Europe. The nature park is characterised by mixed forest, grassland and wetland biotopes as well as a raised bog. Numerous streams radiate in all directions of the compass. One of the main watersheds in Germany runs by Grebenhain. Among the rivers that rise in the Vogelsberg are the Schwalm and Lauter, which are part of the Fulda basin and thus the Weser river system, and the Nidda, Nidder and Wetter which are part of the Main basin and thus part of the Rhine catchment, as well as the Ohm, which drains via the Lahn to the Rhine.