Hardtberg, Mountain summit in Wuppertal, Germany

Hardtberg is a 238.1 m high elevation on the border between Elberfeld and Barmen, its ridge running about 2 km west to east and up to 900 m wide. The summit holds Wuppertal's main park, the Hardt, along with the Elisenturm and the Bismarckturm observation towers, plus the buildings of the Kirchliche Hochschule and a former prison officers' school.

The mountain appears in written records first in 1593 and has long been part of the area's landscape. From 1812 to 1837, it housed the only recorded windmill ever built in what is now Wuppertal.

The name Hardt comes from an old German word for a wooded height; a 1593 document calls the hill "ein geholz die Hardt". In the early 19th century it was nicknamed the "Holy Mountain" because the Barmer Mission, founded in 1818, had its home here. The name is still used mainly around the Kirchliche Hochschule.

The Hardt ridge lies on the border of Elberfeld and Barmen, with the park paths and both towers reached on foot; the ridge runs about two kilometres west to east. The Hardthöhlen caves are protected and closed to the public, and the sealed Cold War tunnel at the Hardtufer is not accessible either.

The Hardthöhlen beneath the ridge are Wuppertal's most important caves and are closed to the public as a nature reserve. In the 1960s a tunnel was driven into the slope at the Hardtufer for a cavern power station meant to survive an atomic attack; the rock yielded too little water, the project was abandoned and the tunnel sealed. Since 2015 the Kluterthöhle association has looked after it.