>>508574478
A bunch of Italians scanned the ground around it with untested tech that does not work on solid surfaces beyond a few feet. So they claim that they measured vibration of water and came up with a bunch of heatmaps. They extrapolated it into columns hundreds of feet deep in the bedrock.
If they want to put more weight into their ubstanciated claims they can scan a known underground location like Paris tunnels or any old mine. But they don't do it and just roll with the story among the alternative archeology crowd, content with the attention they're getting instead of proving it for sure