Lombrives

Grotte de Lombrives or Lombrives Cave is a large natural cavern located in Ornolac-Ussat-les-Bains, at the eastern edge of the Pyrénées Ariégeoises Natural Regional Park, in the Ariège department of Occitanie, in southwestern France. It is still advertised as "the largest cave in Europe" on their website, but in 2017 the cave came under new management and a new website was created which removed the former's fantastically exaggerated statements, including a non-existent Guinness World Record. Those exaggerations persist online on numerous other web pages.

Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).