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We've seen over-the-top penthouses, but the Collector's Penthouse takes opulence to another level thanks to its subterranean element. This distinctive package deal in Chicago includes a 2,537-square-foot designer condo and a 2,700-square-foot underground showroom.

Both are located in the architecturally significant Lake Point Tower -- a luxury building with more than 2 acres of private, wooded grounds on swanky Lake Shore Drive -- one of the most prestigious addresses in the city.

Listed for nearly $4 million, the asking price may seem steep, but when you consider the total package, a penthouse with its own showroom warrants a premium.

The penthouse living spaces are lovely with a contemporary style, open floor plan, and stunning views of the city, lake, and beyond. There are two bedrooms and two bathrooms.

But it's the subterranean showroom that really ups the ante. Configured with tight security and climate control, it was created to exhibit precious collections. The homeowner has approximately $15 million to $20 million worth of vintage Ferraris and Porsches on display down there, with a 1953 Ferrari 340 MM Competition Le Mans Spyder as the crown jewel. The showroom also features a wet bar and a built-in Bang & Olufsen sound system.

We were curious about how this amazing underground spot came to be. Listing agent Daniel Stevenson of The Agency told us the homeowner knew the building's developer. He purchased the deeds to 14 parking spaces along with the penthouse condo. He proceeded to wall in 12 of the spaces, install plumbing and climate control, and add designer decorating touches that suited his car collection. Thus the ultimate man cave was born. As for the remaining two parking spaces? That's where he parks his daily drivers, of course.

If this property were in Los Angeles, the fancy car capital of the free world, it would have already sold -- especially considering the condo fees are only $1,641 per month. But Chicago is a different market, according to Stevenson. He says Midwesterners are a bit more conservative and traditional. "This property is like a shiny, ostentatious emerald in a sea full of diamonds," he says.

The subterranean space isn't limited to auto-related uses. Stevenson envisions it as the perfect place for an art, jewelry, or costume collection. They're marketing it to designers such as Nicole Miller, who might enjoy a presence in Chicago, with a posh living space upstairs and a private atelier below.

We also see it as ideal digs for Oprah, now that she's sold many of her properties in Chicago. If she wants to keep a toe dipped in the Windy City, she could transform the showroom into a supreme closet.

The current homeowner is the head of a production design company that oversees corporate events and private celebrations for huge clients. He races the cars in his collection, in road rally events like the Mille Miglia, a 1,000-mile Italian race from Brescia to Rome. His wife is also a trained race-car driver and often serves as his navigator.

So where will this well-wheeled couple land once they sell their top-to-bottom spread in Chicago? Where else but the fancy car capital of the free world? L.A., of course.