reporter: from secret passage ways aboveground to an entire world below. you see, seafood importer want aid really beg house. and when zoning laws wouldn t let him build up, well john? went down. way down. five stories belowground. we re approaching 20 feet below the ground. i feel like we re in another world. at the end of the labyrinth, two stories below ground, well everyone needs a hamam, right? a hamam is a wet spa. reporter: i don t know what to say right now. i am kind of speechless. this is all 24 carat gold. you can do a mud bath in the subterranean level of your spa. everybody needs a mud bath. what is an underground mansion without a tennis court made to u.s. open specifications of course, 50 feet below ground big enough to double as a ballroom. it can withstand a pretty