The most amazing 'complex' I've ever seen is the top of the lid of a 65,000 (+) wine barrel room just north of Santa Rosa, (Sonoma County) California. For the barrel room the contractor dug this hug hole in the ground, they then roofed same and put 10 some feet of earth on top of that.
Now what? Some one apparently asked 'How big is that?' End game were four full sized (regulation) soccer fields. That give you a clue as to how many barrels of wine are stored below?