A mountain in the Algerian Sahara, known as Taourirt Tan Afella, continues to be a site of concern for scientists more than six decades after a French nuclear test conducted there in 1962. The test, code-named Béryl, was an underground nuclear explosion intended to validate a prototype for future Mirage IV bombers, a key component of the nascent French nuclear deterrent. The test was conducted in a spiral gallery carved into the mountain, designed to contain the explosion's radioactivity within the rocky massif. However, the explosion proved more powerful than anticipated. The spiral gallery did not collapse as planned, and the closure system failed, leading to the release of a radioactive cloud that reached up to 2,600 meters in altitude. The fallout was detectable hundreds of kilometers from the site, with estimates suggesting that about 5 to 10% of the total radioactivity generated by the shot was dispersed into the Saharan atmosphere. The incident affected more than 100 people on-site, including Pierre Messmer, then Minister of Defense and future Prime Minister, and Gaston Palewski, Minister of Scientific Research. Nine soldiers from the 621st Special Forces Group received radiation doses up to 600 mSv, a level considered dangerous for health. Additionally, more than 5,000 residents of the Hoggar region, along with nearly 2,000 military and civilian workers, and a thousand local workers hired for the tests, were affected by the fallout. Despite the significant human toll, France has not carried out any deep decontamination operations on the site since 1962. The mountain still bears visible traces of the accident, with blackened marks on its granite flank. Radioactivity measurements from the time, recorded by two scientists, remain classified in secret archives, raising questions about the actual extent of contamination and the long-term health consequences for local populations. The Béryl test highlights the risks associated with underground nuclear testing and the long-term environmental and health impacts that can result from such tests. The site remains a symbol of the unresolved issues surrounding French nuclear history and the legacy of colonial-era nuclear testing.