Hardthöhlen, Cave system in Wuppertal, Germany

The Hardthöhlen is a cave system beneath Hardt Park in Wuppertal that runs through limestone layers underground. The system consists of passages of varying widths and heights that form a branched network.

The cave system formed over long periods as water dissolved limestone and gradually shaped the passages we see today. During World War II, local residents used a section as shelter during air raids.

The caves are protected as a nature reserve, a status first granted under the Reich Nature Protection Act of 1937/38 and confirmed by North Rhine-Westphalia on 23 June 1966 because of their species-rich cave fauna. The city of Wuppertal tasked the Arbeitskreis Kluterthöhle e. V. with looking after the caves, which remain closed to the public.

The caves are not open to the public, so there are no guided tours; access is limited to authorised researchers and members of the Arbeitskreis Kluterthöhle, which the city of Wuppertal tasked with looking after the system. The entrances lie beneath the Hardt-Anlagen park on the Hardtberg. The connecting passage between the upper and lower caves was rebuilt to make the traverse safer.

The cave system holds fossils of nautiloids, an extinct sea creature, preserved in the lower limestone sections. These finds show that the area was covered by ocean millions of years ago.