The secret operation beneath Lord Airey's Battery

Lord Airey's Battery is located near the southern end of the Upper Rock Nature Reserve in Gibraltar. It is named after General Sir Richard Airey who served as Governor of Gibraltar from 1865 to 1870. Construction of the battery started on 25 July 1890 and was finished by 1 March 1891. The battery was initially armed with a 6-inch breech loading gun, but a 9.2-inch Mark X BL gun was later installed in 1900. In late 1996, after searching for more than two years as a team, the Gibraltar Caving Group unearthed a secret complex in close proximity to Lord Airey's Battery, which was the site of Operation Tracer. The facility was constructed for the secret, World War II military operation to support six men, and provisions for seven years were later supplied.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons