This section gathers virtual tours of underground locations, including the tomb of Ramesses VI, the Serapeum of Saqqara, Roman catacombs, and Père Lachaise cemetery crypt. It features engineering sites such as Maltese limestone cisterns, the 1870s Caluire reservoir, the Bicêtre hospital well, the Harnekop nuclear bunker near Berlin, and Parisian underground quarries. Readers learn about the history, architecture, and scientific uses of subterranean structures across different historical periods.