Over on industrytap.com, "This 5,000-Year-Old Underground City was Just Unearthed in Cappadocia, Turkey." Learn more here.
Also, on brightside.me, "A Real Underground Kingdom" is the subject of an excellent pictorial here.
Finally, on extremetech.com, "Scientists discover an ocean 400 miles beneath our feet that could fill our oceans three times over." Find out more here.