The owner of a lavish 1930s Georgian mansion in Melbourne, Australia recently faced the problem of needing to build a garage to accommodate his (or her, but we're just assuming it's his) collection of very expensive cars without detracting from the beauty or style of the house itself. He dealt with this problem in the way that only a person rich enough to own that house in the first place could: he built a recreation of Bruce Wayne's underground Batcave. The entrance is hidden under the hydraulic floor of a tennis court, of course.
Honestly, looking at the pictures, the only question we have is why every billionaire doesn't have one of these things. Or why more billionaires don't take their cues from Bruce Wayne for all manner of accessories and amenities. According to some recent calculations, the cost of turning yourself entirely into Batman would be around $682,450,750, which is little pricey even for a billionaire. But the Batcave seems doable.