Alexei Sayle mentioned these tunnels in his autobiography "Stalin Ate My Homework" - I wasn't sure he was being completely serious.
[NB I strongly recommend the audio version of the book as Alexei narrates it]
Well that is some H.P. Lovecraft material right there...
My thoughts as well. Let's hope they don't finish excavating the tunnels and accidentally walk the path in the wrong pattern. Who knows what hidden realm you'd end up in.
This reminds me of a story I saw a while back about people apparently becoming obsessed with tunnel-digging for its own sake. I can't seem to be able to dig up the story itself, but https://en.wikipedia.org/wiki/Burro_Schmidt_Tunnel was one of the cases mentioned in it.
This sounds fascinating. If you or anybody else can find the article please post it!