There’s a good stat that shows how popular iceberg houses are in London. In the last ten years, if you were to combine the amount of earth carved out to make way for expensive basements under the capital, it would amount to 50 times the height of the Shard. Hidden from view, the city is filled with secret square footage. The phrase “unusual celebrity basements” is best left ungoogled, but of the one-percenter houses that don’t have sinister activity going on, there are some thoroughly innovative and enviable pads to make you question the size of your home (the average floor space in a UK flat is a meagre 43 square metres).

An underground pool built by the London Basement company

Damien Hirst leads the pack with a 150ft basement conversion under his Grade-I-listed, £40 million mansion in Regent’s Park. The extension features a 25m swimming pool, sauna and steam room, in addition to a yoga room. It took four years of battling the council to build. The main feature of Hirst’s basement, which has yet to be publicly photographed, is to house his private art collection of 3,000 pieces in double-height ceilings, which, as a metaphor for the current state of the art world, is pretty neat.

“We’ve heard of requests for rifle ranges, full fashion runways,” Robert Wilson, the director of Granit Architects, a popular iceberg house firm, once told an 

. “There’s a trend, or so I’ve heard, where people like to swap their artwork … and if they have a large piece, they often need an elevator to transport it to their basement gallery.”

“Luxified troglodytism” is how one academic 

 of iceberg houses describes it, assessing that over the course of a decade (2008-2017), 4,650 basements were granted planning permission. Of those, 112 have been “mega” basements — meaning three or more storeys — which tend to be in the Westminster and Kensington and Chelsea areas.

A Mayfair pile on sale with Saville’s (POA) with a pool extension

Popular requests for mega basements are pools, gyms, wine cellars, dining rooms, cinemas, libraries, recording studios, bars, and, somewhat depressingly, subterranean staff quarters. Iceberg construction peaked when west London councils limited excavations to one storey, and less than 50 percent of the garden. This will come as a relief to residents — a couple of years ago, a £6m Chelsea townhouse collapsed during a basement dig-out — and heralds an end of a more lavish era in construction. Those who got in under the wire include the billionaire Len Blavatnik, whose Kensington Palace Gardens basement has a multi-storey car park, and Jon Hunt, the founder of Foxtons, who also has a collection of classic vehicles in his four-storey basement.

Not everyone wins. David Graham, the Canadian TV tycoon, tried to triple the size of his Knightsbridge mansion by building a ballroom, gym, swimming pool, sauna, massage room, wine cellars, art storage facility, garage, car lift, and staff quarters, but was turned down. The Duchess of St Albans, a neighbour, complained that these plans were “monstrous and unnecessary”.

You have to cross the pond to find houses that have really outrageous amenities. Tony Hawk, in the backyard of his SoCal home, has a 4,000 square foot skatepark. John Travolta’s Ocala, Florida pile has a 7,500-foot runway leading to his front door. Lil Wayne’s old Miami home has an indoor pool for sharks. Ron Howard’s Connecticut estate has its own space observatory. DJ Khaled has a shoe closet big enough to fit 500 pairs of sneakers. Bill Gates, at Xanadu 2.0, has a trampoline room with 20ft-high ceilings. Paris Hilton has a separate mansion for her dogs, costing $300,000. Lady Gaga has a bowling alley. Nicholas Cage’s Las Vegas crib has a “crow dome” to allow his pet bird to flap about in luxury. We clearly need to dream bigger.

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