[arjie]

Are there places in the world where this is still possible? I.e. relatively in a state of order but where enforcement of this kind of thing is poor.

[defrost]

Sure, 4 Ha (10 acres) is an inconsequential corner of a 4,500 Ha farm with rural zoning - no one's going to care if you carve out a few underground spaces and rock wall them entirely and only at risk to yourself.

Community standards kick in once you open such things to the public or move to sale w/out disclosing an invisible (or plainly visible) potential hazard that the buyer should be aware of.

Well, in rural Australia at least.