> An illegal tunnel in a densely populated city like that is a bold move.

I'd say it was an utterly braindead move and pretty much everyone involved is lucky to be alive.

There's just so, so much dangerous stuff you can hit below ground - high voltage cables that really, really do not like it if you even nick them, high current cables giving off nasty electromagnetic fields, ordinary low voltage cables whose isolation is already degraded, old water, gas, steam and sewer mains that may or may not burst simply because the only thing holding together the rust is the pressure from the soil, other, maybe long forgotten tunnels...

And that's before even getting into the issue of potentially getting caved in, creating a sinkhole or an ingress avenue for stormwater.