Photo - Hollenloch
© Caveman-AS · CC BY-SA 4.0, https://creativecommons.org/licenses/by-sa/4.0/ · Wikimedia Commons · https://commons.wikimedia.org/wiki/File:Hollenloch_R%C3%B6senbeck_H_00026.jpg
Source: Geotopkataster Nordrhein-Westfalen (Geologischer Dienst NRW) (ogc-api.nrw.de), modified. Data licence Germany – attribution – version 2.0 (dl-de/by-2-0), https://www.govdata.de/dl-de/by-2-0 Geowissenschaftliche Daten: INSP-GeotopeinNRW @ Geologischer Dienst NRW · data as of 2026 · Contains information from Grottocenter (Wikicaves), grottocenter.org, made available under the Open Database License (ODbL 1.0, https://opendatacommons.org/licenses/odbl/1-0/), modified. · depth, length · obtained 2026-11-13 · https://grottocenter.org/ui/entrances/23713 · data as of 2026 · Source: Wikidata – cave items (Germany) (www.wikidata.org), modified. CC0 1.0, https://creativecommons.org/publicdomain/zero/1.0/ Wikidata (CC0 1.0) · names · obtained 2026-11-13 · data as of 2026 · The derived data is available on request under the ODbL: [email protected]