Himmeldunkberg, which consists of basalt and tuff, is located in the southwestern part of the Lange Rhön, which is part of the Hohe Rhön, and is 888 m high. 2 km to the south is the village of Oberweißenbrunn, 4 km southeast Bischofsheim and 3 km northwest Gersfeld.

The former border between the Kingdom of Bavaria and the Kingdom of Prussia runs across the mountain. The boundary stones set in 1872 bear witness to this.

The Rhine-Weser watershed runs across the summit of Himmeldunkberg and the neighboring Hohe Hölle, as does the border between Bavaria and Hesse and the Rhön Heights Trail. The summit is open and padded with the characteristic Rhön bristle grass. From the top of the mountain you have a magnificent view to the Kreuzberg, the Black Mountains, the Dammersfeldrhön as well as to the valley of the Brend and the upper Sinn. From the northeastern flank you can also see the Heidelstein. 

The mountain is located in the nature reserve of the same name. The northern slope falls steeply and is covered with mixed deciduous forest. The southwest to east slope is unwooded. Here grow grasses, silver thistles, bluebells and shrubs such as rosehip and sloe.

The Himmeldunkberg is important for model gliding. In the past it was also used by hang gliders and paragliders. 

At an altitude of 835 m, the Würzburger Hütte (self-supply) is located on the western slope. On the ascent to the mountain, medieval fields are recognizable in flat slopes (Hochäcker). About 50 m south below the summit one finds the natural monument Hexenbuchen. 

The mountain is located on the premium hiking trail "THE HIGH RHÖNER".