Over on smithsonianmag.com, "A Secret Tunnel Found in Mexico May Finally Solve the Mysteries of Teotihuacán." Find out more here.
Also, on spiegel.de, discover "Rome's Tremendous Tunnel: The Ancient World's Longest Underground Aqueduct" here.
Finally, on ancient-origins.net, "Extensive Ancient Underground Networks [have been] Discovered Throughout Europe." Learn more at here.