I wrote a blog post a few weeks ago on "Ancient Tunnels" here but wanted to revisit tunnels again. Over on quora.com, a curious person asked "What techniques were used to construct tunnels, during ancient and medieval times, to meet exactly at the same point midway?" Find out here.
Also, on atlasobscura.com, they tell us "We Still Don't Know Why Medieval Europeans Built Their Mysterious 'Erdstall' Tunnels" here.
Finally, on dailymail.co.uk, they let us know "Tunnels of war: 200-year-old passages where French prisoners were held during the Napoleonic Wars go on sale for £19,000" here.