By CHRISTINE AJUDUAJAN. 17, 2014  The British capital’s evolving skyline is as impressive as it is unusual. Consider the Shard, the 1,016-foot “vertical city” that topped out as Western Europe’s tallest building when it was completed in 2012, and 20 Fenchurch Street (a.k.a the Walkie-Talkie), which made headlines last summer when the glare from its cartoonishly flaring facade warped the panels of a Jaguar parked outside.  Whereas Manhattan is built upon hard rock, London — ancient, sprawling, famously self-deprecating — has its roots buried in a bed of clay, sand and chalk, an unlikely foundation for high-rise grandeur. Rather, as the author Peter Ackroyd noted in “London Under,” “the geology of London is a clue to the labyrinth beneath”: a deeply layered palimpsest. During construction for the coming Crossrail subway, archaeologists have unearthed medieval ice skates, Roman skulls and prehistoric bison bones, all within 12 feet of the pavement. Meanwhile, with sky-high property rates above ground, some of the city’s most innovative art spaces, restaurants, shops and bars have been springing up below street level.  Of course, Londoners have long possessed a downward-cast gaze. Take the Tube — the world’s first underground rail system, introduced just over 150 years ago. Its stations provided shelter when the city was blitzed during World War II; they’ve also displayed commissions by artists from Man Ray to Tracey Emin. Now, the Old London Underground Company is hoping to reopen 26 ghost stations as attractions. Think of elevator-shafts-turned-climbing-walls and 24/7 karaoke clubs where there were once secret war rooms. “There’s nothing more valuable in the world than looking into your old cupboards and finding a toy,” the company’s founder, Ajit Chambers, said.  In the fantasy novel “Neverwhere,” Neil Gaiman depicts an underworld invisible to “London Above,” where the tony neighborhood of Knightsbridge becomes an ominous Night’s Bridge. In reality, with the confluence of wealth in the area and the city’s notoriously restrictive planning laws (generally, those looking to expand their homes cannot build up or out — only down), it is prime territory for digging out multilevel “billionaire basements” to house, say, a tennis court and a personal car museum.  Following suit, a sleek, 85-room Bulgari Hotel opened here a year and a half ago with six subterranean floors for the restaurant, ballroom, cinema, spa and glittering glass-mosaic swimming pool, the jewel in an inverted crown. There’s even a plan to convert an underground parking lot in Bloomsbury into a budget hotel with 172 windowless guest rooms. Pending a green light, it’s one of many new schemes to repurpose parts of London often overlooked. Here are some of those projects, along with places you can visit now.  Hailed as the “Eighth Wonder of the World” when it opened in 1843, the Thames Tunnel — forerunner of the Tube, burrowed by Marc and Isambard Brunel as an under-river path for horse-drawn carriages — was soon overrun by criminals and closed to pedestrians for nearly 150 years. Now, the Brunel Museum offers guided descents into the tunnel’s Grand Entrance Hall and plans to turn the sooty underground shaft into a proper amphitheater. Last year it started hosting concerts from the likes of the Pop-up Opera company, which will pop down again come spring.  Countless passageways, many long abandoned, lie beneath London. Off the graffiti mecca that is Leake Street, under Waterloo station, an 18,000-square-foot labyrinth of disused rail tunnels will be opened later this month for Vault 2014 — a six-week immersive arts festival, Jan. 28 to March 8, with more than 60 acts (including a surrealist adaptation of “Fear and Loathing in Las Vegas”) and late-night parties. “It’s piercing the constructed armor of the city that delineates where you’re allowed to have your fun,” said the festival’s co-director, Tim Wilson.  The Establishment has been going underground, too. In 2012, Tate Modern unveiled the Tanks, a live art space occupying the former power station’s three subterranean oil chambers (while currently shut for the building of a 10-level extension above ground, they’ll reopen by 2016). And for its biggest exhibitions the Victoria and Albert Museum — which has long staged its cutting-edge shows in three rooms, housed in two 19th-century courts and separated by a corridor — has tapped the local firm Amanda Levete Architects to design an open-plan gallery about 60 feet below its new courtyard, all scheduled to open in 2017.  Another Victorian landmark, the 46,000-square-foot Shoreditch Town Hall, site of the inquest into Jack the Ripper’s last murder, has turned its maze of dilapidated basement rooms into a venue for experimental arts. Called the Ditch, it kicked off in July with a cabaret festival.  Under a parking lot nearby, archaeologists have discovered London’s second-oldest and best preserved Shakespearean playhouse: the 16th-century Curtain Theater, or the “wooden O” that premiered “Henry V” and “Romeo and Juliet.” “Digging down in London is like going back in time,” said architect John Drew, of Pringle Brandon Perkins+Will. With input from the Museum of London Archaeology, his firm is designing the Stage, Shoreditch — a large-scale regeneration plan including a 13,000-square-foot exhibition and performance space set to open around the excavation site within five years. Remnants of the theater will be displayed in-situ, 10 feet below ground.  More and more establishments have been inspired by their own underground histories. Last September, the Royal Academy of Arts opened its 19th-century Keeper’s House — never before accessible to the public — with a seasonal British restaurant designed by Sir David Chipperfield and Rolfe Kentish in the formerly unused basement. Previously the kitchen and scullery, it was, before that, the servants’ quarters, a beer store and a 17th-century crypt with a wine cellar, now a vaulted ladies’ room. In the dining area, with its cream-leather furnishings and 18th-century casts, the walls are lined with a billiard-table baize that stops short of the exposed-beam and brick-hearth soffits.  In Soho, the just-opened Coal Vaults is situated within a 19th-century subterranean coal storage facility. Here you’ll find low-lit, exposed-brick dining vaults and a copper-topped bar, plus small plates (deviled popcorn; venison sliders with shallot rings) and cocktail pairings.  Nearby is Brasserie Zédel, which at first glance seems to be merely a small cafe from the owners of the Wolseley. Its street-level facade belies the 11,220-square-foot restaurant-bar-cabaret complex humming in the depths of the former Regent Palace Hotel, Europe’s largest upon opening in 1915. Down a grand, winding stairwell adorned with retro carpeting and vintage French posters, the brasserie — with its all-day, en français menu — is an Art Deco homage to its precursor via Jazz Age Paris. Gilded and marble-clad, it’s also part of a local restoration project overseen by the Crown Estate.  “We actively avoid the sites that most restaurateurs would describe as prime,” said Huw Gott, co-founder of Hawksmoor, a group of clubby British steakhouses mostly set below ground. Its latest location — a level-two spot on Air Street, near Piccadilly Circus — is an anomaly, but the windows have been blurred and darkened with stained glass. “The aim is for customers to come in and forget the outside world,” Mr. Gott explained. Previously a “dodgy strip club,” the Spitalfields cellar bar — which serves cheeseburgers with ox cheek (£9.50, or $15) in turquoise-tile dining alcoves — was a natural fit. “We like off-pitch,” he said.  Apparently, so does the team behind the Attendant — a coffee shop in a Victorian “gentlemen’s loo” that had been lying unattended below Foley Street in Fitzrovia for half a century. After an industrial scrub, it reopened last year, offering almond-milk porridge, salt-beef bagels and Jaffa cakes, with bright-green barstools facing the original porcelain urinals. (The kicker: There’s no bathroom.)  It’s been said that from a window in the Selfridges basement you could see a perfectly preserved Victorian high street. This is a myth, according to a spokesman for the department store, though the “sub” and the “sub-sub” — going nearly 200 feet below ground — did shelter 50 United States Army Signal Corps soldiers during World War II, with remnants of prison cells at the bottom. While they’re off limits to customers, the regular basement is now staging a six-week Festival of Imagination, through March 2, with a mirror-clad “Imaginarium” designed by Rem Koolhaas for talks by “imagineers” like the Swedish electronica band Little Dragon.  In Shoreditch, the avant-garde fashion boutique Hostem has repurposed its cellar as the Chalk Room, a by-appointment store-within-a-store for bespoke offerings such as made-to-measure Casely-Hayford suits and custom umbrellas from Oliver Ruuger. Swathed in off-black chalk paint, the space — designed by the husband-and-wife team JamesPlumb with haunting one-off assemblages (including a restored 19th-century wardrobe, tipped to one side) — is itself worth a trip down the creaking, burlap-covered stairs.  The otherworldly, appointment-only Late Night Chameleon Cafe (LN-CC) occupies the basement of a nondescript warehouse farther east in Dalston. Down a side alley and a dark flight, you step into a forestlike tangle of branches that opens onto a brushed-concrete Warmth Space, showcasing fashion-forward labels like Haider Ackermann, and a recently added Secular Space, one silver neoprene tunnel displaying futuristic bags and footwear. A colorfully lit, hexagonal passageway leads to the new Sound Space and mezcal bar, where this reporter attended an interactive music night featuring an improvised analog synthesizer set.  Speakeasy-type bars have been cropping up all over town — below a Breakfast Club cafe in Spitalfields (ask to see “the mayor”) or a BrewDog in Shoreditch (UnderDog, downstairs, serves beer cocktails in addition to pints). Hidden under a juice bar in Covent Garden, the tiny, candlelit B.Y.O.C. (Bring Your Own Cocktail) requires guests to bring a bottle of liquor: the mixologist, pushing an antique trolley with ingredients from upstairs, will need it to fix your drink. B.Y.O.C. does not have an actual bar, or a liquor license.  Some feel that the trend is a bit overkill. “If I hear of another speakeasy coming up, I might literally have to kill myself,” said Mark Holdstock, owner of Bourne & Hollingsworth, a ’20s-style basement bar in Fitzrovia. In 2012, his team started converting a cellar on Goodge Street that, they soon discovered, was the home of a now-deceased vicar. They named the bar after him — Reverend J. W. Simpson — and kept the water-stained wallpaper and peeling paint, adding votive candles and a series of “sermons” on reviving forgotten spirits of another sort.  Nightspots like Disco in Soho have been fashioned as London’s latest see-and-be-seen escapes. At Disco, a ’70s-inspired underground boîte and private members club, you enter through a Pan Am-style lounge complete with airplane doors.  On the opposite end of the spectrum: Ruby’s, situated under an old cinema sign in Dalston. Previously the kitchen of a Chinese takeout joint, it now serves seasonal cocktails in 1940s milk bottles. Nearby, the hipster favorite Dalston Superstore recently opened Dance Tunnel, spinning left-field house and techno under a pizza parlor. “People come in looking for the ‘secret entrance,’ ” said Dan Beaumont, a co-owner, though the venues sit down the road from each other. “Usually they end up trying to get into a storage cupboard.”  Bulgari Hotel, 171 Knightsbridge; bulgarihotels.com.  Brunel Museum, Railway Avenue, Rotherhithe; brunel-museum.org.uk.  Vault 2014, the Vaults, Leake Street; thevaultfestival.com.  The Ditch at Shoreditch Town Hall, 380 Old Street; shoreditchtownhall.com.  Keeper’s House, Royal Academy of Arts, Burlington House, Piccadilly; keepershouse.org.uk.  Coal Vaults, 187b Wardour Street; coalvaults.com.  Brasserie Zédel, 20 Sherwood Street; brasseriezedel.com.  Hawksmoor Air Street, 5a Air Street; Hawksmoor Spitalfields, 157a Commercial Street; thehawksmoor.com.  Attendant, 27a Foley Street; the-attendant.com.  Selfridges, 400 Oxford Street; selfridges.com.  Hostem, 41-43 Redchurch Street; hostem.co.uk.  LN-CC (store closed for refurbishments until Feb. 1), 18 Shacklewell Lane; ln-cc.com.  The Mayor of Scaredy Cat Town at the Breakfast Club, Spitalfields, 12-16 Artillery Lane; themayorofscaredycattown.com.  UnderDog at BrewDog Shoreditch, 51-55 Bethnal Green Road; brewdog.com.  Reverend J. W. Simpson, 32 Goodge Street; revjwsimpson.com.  Disco, 13 Kingly Court; disco-london.com.  Ruby’s, 76 Stoke Newington Road; rubysdalston.com.  Dance Tunnel, 95 Kingsland High Street; dancetunnel.com.  A version of this article appears in print on January 19, 2014, on page TR1 of the New York edition with the headline: An Underworld Comes to Life. Order Reprints|Today's Paper|Subscribe
A descent into the city’s subterranean spaces can lead urban explorers to everything from culture to cocktails to cuisine.