Grotte de Rosée
The Grotte de Rosée (Cave of Rosée) is located near Éhein in the municipality of Engis, in Belgium. It has been classified as Wallonia's patrimoine immobilier exceptionnel de la Région wallonne (exceptional heritage of Wallonia'), and can be visited only by accredited scientists. It houses a set of concretions which is unique in Belgium.
Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).