Holtorfer Hardt, Mountain summit in North Rhine-Westphalia, Germany.

Holtorfer Hardt is a wooded elevation of 150.8 m above sea level on the Ennert ridge in Bonn's Holtorf district, also called Ennert-Hardt to distinguish it from the Dollendorfer Hardt. Its western slope is forested, and the Hardt is crossed by Pützchens Chaussee and Oberkasseler Straße. On the hill are the Hardtweiher pond, a hunting-research station with a wildlife enclosure, a viewpoint and a hiking hut; Niederholtorf lies on the eastern slope.

On the western slope of the Hardt, three burial mounds from an earlier period were found. Around 1800, lignite was mined in the Ennert; in 1807 Leopold Bleibtreu identified a seam about 1.5 m thick from which alum could be extracted. Two Bleibtreu alum works and Matthias Jäger's plant processed the coal on the Hardt, underground mining began in 1835, and in 1853 the firms merged into the Bonner Bergwerks- und Hütten-Verein AG. Output declined from 1863 and stopped in 1876; the alum works were largely demolished, their stone used for the first church in Niederholtorf.

The name Hardt, used for several wooded hills in the area, distinguishes this one as the Holtorfer Hardt or Ennert-Hardt. On the Hardt stand a pond, the Hardtweiher, a game enclosure belonging to the research centre for hunting studies, a viewpoint and a hiking hut. The Alaunbach and Teufelsbach flow north off the hill, the Ankerbach south.

Several hiking routes reach the summit from Sankt Augustin and surrounding towns, with varying distances and difficulty levels depending on your choice. The marked trails pass through or near small residential areas, making navigation straightforward.

Three burial mounds were found on the western slope of the Hardt, evidence of early use of the hill. The name Hardt distinguishes it from the Dollendorfer Hardt and another Hardt further south, so it is also called Holtorfer Hardt or Ennert-Hardt.