I was in Kansas City on business and one day at lunch my colleagues and I stumbled onto Subtropolis. Subtropolis is a limestone mine dug into the side of a hill which is being converted to office space as it is emptied of rock. It's only partially completed but already has a confusing network of streets and train tracks running through it. They say that when it's done it'll have enough square footage to accommodate all of downtown Kansas City.

According to the FAQs on the Subtropolis web site (http://www.huntmidwest.com/advantage.html), the principal advantages of locating underground in rock are low utility bills (it's 65-72 degrees inside year-round), "security", and the absence of leaks. The FAQs don't mention the obvious risk of vitamin D deficiency; perhaps they plan on installing milk machines every couple hundred feet, or supplying each lessee with one or two special subterranean, eyeless cows. Indeed, in fairness, management appears to value fitness highly -- every year, Subtropolis hosts the world's largest underground 5 and 10K race, the "Ground Hog Run".

Subtropolis is owned by Lamar Hunt, whose other holdings include the Kansas City Chiefs and the Kansas City Wizards (soccer). Lamar's brother Bunker has what might be called a nominal stake in the enterprise but I can't tell if he's invested any money.

Here's a typical office inside Subtropolis: