Going underground is all the rage these days, with a tricked-out basement an absolute must for the savvy ultra high-net-worth homeowner looking to add value to their property. From basement swimming pools and supercar galleries, home gyms and luxury cinemas to a below-ground village and even a copycat Batcave, feast your eyes on the world's most awesome basement spaces.

Billed as one of California's most extravagant homes, Hacienda de la Paz in Rolling Hills near Los Angeles features what has to be the most achingly beautiful basement in America. The former owner, frozen food magnate John Z. Blazevich, circumvented strict local planning regulations by building down, creating a palatial Moorish-inspired hammam complete with a pool that looks like it belongs in Spain's mesmerising Alhambra palace.

As well as housing the dreamy hammam, the basement also incorporates a magnificent 15,000-square-foot tennis court that doubles up as a ballroom. In contrast to the Moorish-style spa, the space has an 18th-century Baroque vibe. According to reports, it is large enough to accommodate 350 sit-down guests for dinner, hundreds more for a ball, as well as a 30-piece orchestra.

In addition to the basement, Hacienda de la Paz features nine bedrooms, 25 bathrooms, a myriad of reception rooms, a gym and yoga room, an outdoor swimming pool, and a whole lot more besides. Despite its many amenities, Blazevich struggled to sell the property and eventually offloaded it at auction in 2018 for $22.4 million (£17.1m), 50% less than the original asking price.

This ridiculously luxurious basement is located beneath an incredible ski chalet in the high-end Swiss resort of St. Moritz that was “designed to make a billionaire's jaw drop”, according to an interview with listing agent Senada Adzem. The space, which is connected with secret tunnels, certainly doesn't disappoint.  A breathtaking complex, it's loaded with the most deluxe amenities money can buy.

The highlight of the opulent basement is most definitely the underground lake. No mere swimming pool, the spectacular amenity has a ceiling designed by artisans in Venice, glistening mirrored walls and underwater Swarovski crystal lights.

The sprawling lake covers a large swathe of the basement. From this particular angle, the freestanding floating staircase that links all five levels of the property, a feat of architectural ingenuity if there ever was one, can be glimpsed, together with various chill-out areas.  

Just to the side of the underground lake is a huge hot tub. The basement also features a wonderful spa with a sauna, subzero ice chamber, Turkish bath, pink Himalayan salt room and massage area, the perfect place to head to after a day's skiing or snowboarding on the pistes.

Pictured here is the all-white Turkish bath. Unlike the rooms upstairs, which are heavy on ostentatious features such 24-karat gold plating, mink and Loro Piana-designed cashmere walls, rare marble, outrageously expensive bespoke artworks and the like, the space is starkly minimalist but no less luxurious.

The subterranean wonder also packs in a state-of-the-art climate-controlled wine cellar, a supercar garage and a capacious home cinema with red velvet seating that cost $1.3 million (£993k) to install. As you might imagine, the six-bedroom, six-bathroom ski chalet, which is called 'La Lonsdaleite' or 'The Ice Palace', doesn't come cheap: the property was listed with Senada Adzem in 2017 for a cool $185 million (£141.4m).

The star attraction though has got to be the basement swimming pool. Bathed in light thanks to its glorious glass ceiling panels, the fabulous feature boasts grand columns, exquisite mosaic tiling and a wall dotted with twinkling LED lights. The pool forms part of the lower-ground spa, which also rocks a sauna, steam room, hot tub and treatment room.

Adjacent to the showstopping swimming pool is this stunning speakeasy-esque bar. The seductive space packs in a high-end pool table, premium built-in cabinetry and plenty of finely upholstered seating on which the lucky owner and their friends can kick back and enjoy a cocktail or glass of champagne.

The wow-factor amenities of this decadent basement don't stop there. The lower-ground level also has its very own bowling alley, which must be one of the poshest on the planet. Between games, the well-heeled bowlers can relax on the comfy leather sofas or nip to the bar for a drink. 

And if the aforementioned features weren't enough to entice a billionaire buyer for the property, which is on the market with Sotheby's International Realty, the basement also houses an Art Deco-style home cinema with plush velvet seating, leather walls and a sensational fibre-optic star ceiling. The lower-ground level has a lounge and self-contained staff quarters to boot. What more could a moneyed house-hunter ask for?

The great room of this megamansion in Lake Quivira, Kansas offers a tantalising clue as to what lies hidden beneath its floor. Built in 1992 at a cost of $30 million (£22.9m) for Dennis Langley, the late founder and CEO of the Kansas Pipeline Operating Company, the fantastical property, which he christened The Spirit of Avalon, is inspired by the legend of King Arthur.

The basement conversion is nothing short of a paradise for the scuba-diving enthusiast. Buried 30-feet deep, the vast network of hidden tunnels extend under the entirety of the property, as well as below the surrounding grounds and into the mountain that is situated next to the megamansion.

Langley also constructed an extensive wine cellar beneath his one-of-a-kind megamansion. Other features of the property include commercial-grade chef kitchens, a library, games and conference rooms and acres of grounds. It is on the market right now with Crown Realty for the relatively bargain price of $10.9 million (£8.3m).

Luxury home cinema firm Elite HTS didn't hold back with this sensational Dark Knight-themed Bat Cave home cinema, which the company conceptualised in 2014 for “a reclusive client' for the basement of their Greenwich, Connecticut mansion. The cost? An eye-watering $2 million (£1.5m).

To access the unbelievable home cinema, the homeowner enters a secret lift located behind a grandfather clock at the back of a private study. Bursting with security features, the lift has a fingerprint and retina scanning system to ensure only the owner can enter the subterranean Batcave.

Measuring a total of 12,000 square feet, the home cinema stuns with six life-sized replica Batsuits along with a garage housing a copycat Batmobile and escape tunnel, which is hidden behind a sliding bookcase door.

Perfect in every detail, this shrine to the Caped Crusader is worthy of any superfan. Other features of The Batcave home cinema include an Austrian-made 283-foot 4K screen and racecar-inspired leather seats, each of which have Crowson amplifiers, actuators and transducers built in to offer a 4D movie experience.

The basement of this imposing six-bedroom, six-and-a-half bathroom mansion in Fort Mill, South Carolina is quite unlike any other in the world. Amazingly, the subterranean space houses an entire village entertainment area complete with evocative storefronts, a star ceiling, and so much more.

There's a fantastically retro soda shop, which has diner-style seating and lighting, a kitchen with soda fountains, and a magazine display jaw-packed with classic titles including age-old copies of Life and Action Comics.

Elsewhere in this mansion's basement tiny town is a charming toyshop chock-full of fun playthings and an arcade with a games cabinet that no doubt plays classics like Pacman and Space Invaders, along with a vintage pinball machine.

Inside, the home cinema has a large movie screen with Egyptian statues on either side, eight leather-upholstered seats and a star ceiling. Needless to say, the mansion wasn't on the market for long before it was snapped up earlier this year with the buyer paying just under $1.5 million (£1.2m) for the magical property.

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