This make my brain make an odd poit sound. Assuming that they didn't buy the land, did they actually lease rights to the underground portion, or are those something that's not really existing? I mean really, if I have the tunneling equipment, what's to stop me from tunneling under my neighbor's property and putting in a big underground facility there?
Or in the more canoodling question, when you buy land, just how far up and down does your ownership go?
For instance, I can't tell the airport that no airplanes can fly over my property; effectively, the airspace over 1000 feet is controlled by the Federal Aviation Administration. And in most cities that are zoned for single family dwellings, there are height restrictions placed on the primary domicile of 50 feet or less; the latest I've heard was 35 feet.
I can probably put up some kind of a tower or other structure that's higher, but I'm not at all unlimited.
So how far can I dig down? Certainly the water table puts a damper on any kind of livable construction, but things like a heat pump or geothermal system routinely deal with hundreds and sometimes thousands of feet. My basement is probably 40-50 feet above the water table considering my proximity to the lakes, and that leaves a lot of room for things like underground parking or an underground studio or workshop.
Yes, I know that underground tunnels and facilities take more extraordinary methods of construction. I'm talking more about theory here. What's to keep me from tunneling under my neighbor's yard to increase my available space?