SPOILER ALERT! Spoilers ahead for various Marvel and DC Comics stories.

Eagle-eyed viewers will have noted one of comics’ grooviest superhero lairs featured in the background of promotional posters hyping the CW’s historic four-night TV “Arrowverse” crossover. Beginning in Monday’s episode of “Supergirl,” the crossover stars the main casts of all four Arrowverse shows in an epic battle against a race of alien invaders called the Dominators.

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Standing proudly behind images of the Green Arrow, Supergirl and White Canary is the Hall of Justice, legendary home of the animated Super Friends. Nobody knows how the Hall fits into the plot of the epic event but the fact that it features so prominently in the marketing material suggests it plays a significant role in the struggle against the Dominators. To celebrate the Hall of Justice’s introduction into the Arrowverse, we thought a tour of the coolest superhero lairs in all of comics would be most timely.

16 Mount Justice (Secret Sanctuary)

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Perhaps best known to younger fans as the headquarters of the teenaged heroes of Young Justice, the Secret Sanctuary served as base of operations to several different super-teams over its proud existence. Located in Happy Harbor, Rhode Island and buried beneath the imposing bulk of Mount Justice, the Secret Sanctuary was originally home to the first incarnation of the Justice League of America and also housed the Justice Society of America for a time.

Over the years, despite upgrading a few times to more technologically-advanced digs situated far above the Earth, the JLA did find occasion to return to their first subterranean home. Most notably, the League and their compatriots set up shop in Happy Harbor after Superboy-Prime destroyed the Watchtower during Infinite Crisis. One of the most historic sites in the DC Universe, the Secret Sanctuary helped raise the bar for full-service superhero lairs, adding to a proud tradition of comics’ coolest hallmarks.

Full-Service Amenities: The Secret Sanctuary boasts a fully-functioning jet hangar, gymnasium, meeting chamber and ocean access to the Atlantic for the undersea monarch on the go.

15 Sanctum Sanctorum

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Thanks to the blockbuster success of the MCU’s “Doctor Strange” everybody knows the address 177A Bleecker Street in New York City’s Greenwich Village. Although he hasn’t yet taken up residence at the infamous location in the film, Doctor Strange nonetheless spends a significant amount of time fighting his way through the house’s diverse collection of occult artifacts and esoterica. As one of three other sanctums scattered across the face of the globe, it serves as one of the safeguards against Dormammu’s invasion.

In the comics, Strange has been a long-time resident of Bleeker Street, first setting up shop beneath its shadowy gables in his first appearance in “Strange Tales’ #110. The infamous townhouse serves as a vast repository of arcane knowledge and rests on a focal point of mystical energies. If all that weren’t cool enough, it’s also functioned as a temporary HQ for both the Defenders and New Avengers.

Five-Star Service: Doctor Strange’s long-time ally, Wong, has been responsible for the maintenance and upkeep of the Sanctum Sanctorum for years, ensuring the Sorcerer Supreme and his guests are free to save the world in utmost comfort and security. Plus he cooks a mean bowl of tentacles. Yum!

14 The Carrier

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The sentient shiftship known as the Carrier is one of the most versatile headquarters on our list. Originally an inter-dimensional merchant vessel cruising between universes via the Bleed, the Carrier came into the Authority’s possession after Jenny Sparks discovered it parked in Earth orbit. At 50 miles long, 30 miles tall and two miles wide, it is without a doubt the most massive “super structure” on our list. It’s drive is powered by a baby universe and it essentially exists everywhere at once, granting planet-wide access to the Authority.

Over the course of its storied service, the Carrier has performed beyond the call of duty, providing transportation into the body of an immense cosmic intelligence on its way towards Earth and even evacuating the entire planet to hundreds of alternate realities in a bid to stave off human extinction.

Close to Everything! Thanks to its reality anchor, the Carrier exists in all places on Earth at once, meaning you’ll never have to worry about expensive travel costs!

13 The Legion Clubhouse

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If any superhero HQ on this list captures the sheer, unbridled whimsy of the teenaged imagination, then it is undoubtedly the original clubhouse of the Legion of Super-Heroes. With its retro-futuristic design and charming “Super-Hero Clubhouse” signage, the original Legion headquarters spoke to a generation of readers desperate to suit up and face off against Mordru or the Legion of Super-Villains. Built with the vast financial resources of Legion booster R.J. Brande, the original rocket ship design was eventually destroyed by the Fatal Five.

With an ever-growing membership featuring heroes from across the galaxy, it quickly became apparent the Legion needed much larger digs. Subsequent bases took the form of massive compounds that included vehicle hangars, a training academy and living quarters for the team’s full complement of Legionnaires. Despite all of these new amenities, later Legion headquarters lacked the distinctive charm of the team’s first humble home.

Post-Post-Modern Design: The Clubhouse’s original design was based on the rocket ship that carried Kal-El to Earth. It was also much bigger than it looked from the outside, with numerous underground additions.

12 The Helicarrier

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This old warhorse has been in service in one incarnation or another for decades. First appearing in the classic “Strange Tales” #135, this ultra-cool, Kirby-designed vessel has provided a high-tech, top-secret home for S.H.I.E.L.D. in several different incarnations over the years. Serving as a mobile staging platform for missions all over the world, the Helicarrier is outfitted with a startling array of offensive, defensive and diagnostic capabilities including a compliment of advanced fighter jets, ICBMs and a brig designed to hold the Marvel Universe’s most powerful beings.

Featured heavily in several Marvel movies, a decommissioned Helicarrier was instrumental in the evacuation of the Sekovian capital in “Avengers: Age of Ultron”. Although the Helicarrier has been redesigned, replicated and replaced several times over its history, it continues to be a symbol of S.H.I.E.L.D. power and ingenuity.

Top-Notch Security: Surrounded by an army of highly-trained S.H.I.E.L.D. operatives, your safety and security will never be in question on-board the Helicarrier. Just, you know, ignore all those times it fell out of the sky.

11 The Temple of Atlas

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When former S.H.I.E.L.D. agent Jimmy Woo finally embraced his destiny as the heir to the vast criminal empire of his arch-nemesis, the Yellow Claw’s, he also inherited its labyrinthine base of operations hidden beneath the city of San Francisco. The Temple of Atlas is a marvel of science and magic, where the two traditionally opposing universal forces have been fused together to further the agenda of Woo’s Atlas Foundation.

A permanent home to hundreds of warrior-monks, administrators, laborers and pseudo-science mages, the Temple of Atlas’ main priority is the care of the great dragon known as Mr. Lao, Woo’s scheming, enigmatic advisor. Requiring plenty of naps and a steady diet of cattle to assuage his near-infinite hunger, the Temple of Atlas essentially exists as a hidden city devoted to Atlas’s ancient figurehead. More recently, it has served as a staging area for Woo’s ongoing purge of criminal elements within the Atlas Foundation.

Exotic Nightlife: Situated beneath the streets of historic San Francisco, there’s always something to do in the Temple of Atlas. Do mind the gargantuan, man-eating dragon, though.

10 The Arrowcave

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It could be argued that in many ways, the Green Arrow has always been a bit of a rip-off of Batman. From his origins as a wealthy playboy adventurer to his subterranean superhero lair, there are a lot of similarities between the two characters. In fact, the Green Arrow’s base of operations was swiped from designs originally intended for Batman’s signature headquarters. In recent years, despite some intermittent appearances in the comics, the Green Arrow seems to have distanced himself from his first hideout.

Thankfully, the producers of “Arrow” recognized Ollie Queen’s need for a secret lair and reimagined the Arrowcave as a cutting edge nerve center and training facility. It's an invaluable resource that allows Team Arrow to strike from the shadows with precision and speed, thanks to its cutting edge tech and central location. In a more practical sense, the Arrowcave anchors the TV show around a familiar yet visually dynamic setting, allowing viewers some small measure of continuity – even if it’s been trashed and infiltrated on several occasions.

Free Wi-Fi! Because Felicity Smoak never pays for internet service. Ever.

9 The Watchtower

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The Justice League of America has enjoyed several different headquarters since originally setting up shop in Happy Harbor. There was the iconic JLA Satellite, of course, and the Detroit League’s infamous warehouse HQ that is probably best left forgotten. In more recent years, fans have been treated to the JLA Watchtower, a fan-favorite touchstone of Grant Morrison’s legendary run that re-established the League as the DCU’s elite super-team. Based on a design created by John Stewart and Wonder Woman, the original Watchtower was a base of operations befitting Morrison’s new pantheon of heroes.

Constructed using hybrid alien technology that included Kryptonian, Martian and Thanagarian contributions, the Watchtower was originally located on the moon and featured an extra-terrestrial hydroponics pavilion, a massive aquarium and a well-appointed armory. It was eventually redesigned as an orbiting satellite, tethered via an instantaneous teleportation system to the Earthbound “Hall” in Washington D.C. but never seemed to capture its former glory days as primary residence to the DCU’s most powerful heroes.

Gorgeous Views: When you’re in orbit 22,300 miles above the Earth, the world is literally your oyster!

8 Xavier’s School For Gifted Youngsters

Xaviers School For Gifted Youngsters in Marvel Comics

Xavier’s School for Gifted Youngsters has been destroyed so many times it’s hard to keep track of just how many times the X-Men have rebuilt it. The ancestral home of X-Men founder Charles Xavier, this sprawling estate located in quaint Westchester County, New York has witnessed the Merry Marvel Mutants’ greatest triumphs and most heartbreaking defeats.

A private school unlike any other, Xavier’s is dedicated to training and reintegrating mutants from around the world into mainstream society. Boasting advanced alien Shi’ar tech humming behind its staid, ivy-covered walls, the campus grounds feature an underground hangar for the X-Men’s Blackbird stealth plane, cutting-edge R&D labs, and perhaps the most advanced training facility on the face of the planet in the form of the Danger Room. Xavier’s provides a safe, stable environment, a sense of extended family to its students that is far more valuable than all of its high-tech amenities combined.

Vibrant Campus Life! Learn new life skills with students from around the world in the popular Danger Room, the school’s cutting edge training facility!

7 The Baxter Building

The Fantastic Four's Baxter building

Located at 42nd and Madison in New York City, the Baxter Building has come to symbolize the spirit of hope and innovation heralded by the onset of the Silver Age of comics. One of the Marvel Universe’s most prestigious landmarks as the traditional headquarters of the Fantastic Four, the Baxter Building remains inextricably tied to the colorful history of Marvel’s first family, even if they’ve been scattered across the multiverse in recent years.

More than simply a superhero lair or advanced research facility, the Baxter Building served as a backdrop to the evolution of the FF into one of the cornerstones of the Marvel Universe. This is where readers watched the Richards family grow and evolve, fight their greatest battles and suffer their greatest losses. Recently snatched up by Peter Parker (billionaire “everyman," what!?), the Baxter Building is currently pulling double duty as the temporary headquarters of Parker Industries and the new home of Sam Wilson’s New Avengers team.

Historic Landmark: At 35 stories tall, there’s still plenty of room left in the same building that served as the primary battleground in the Fantastic Four’s first historic encounter with the former World-Devourer Galactus.

6 Titans Tower

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Instantly recognizable, Titans Tower served as the iconic headquarters for several incarnations of the Teen Titans in one form or another. Although it’s been rebuilt at least three times over the years, one thing has remained constant about this imposing structure: its distinctive T-shaped design. A high-tech crashpad originally designed by Cyborg’s dad Dr. Silas Stone, Titans Tower offered a wide array of perks for the young upstart superhero on the go.

Featuring extensive laboratory bays for Cyborg’s many scientific investigations, a great hall and a submarine pen, Titans Tower rivalled the JLA Satellite in security and functionality. The original tower was destroyed by the traitorous Jericho, after surviving for several years as the team’s base of operations. Subsequent builds lacked the bold, in-your-face design boasted by the original tower and failed to resonate with fans and Titans alike.

Instant Curb Appeal: Although it’s more likely to drive the market value of the neighborhood into the ground, there’s something undeniably fetching about this monstrous t-shaped supervillain magnet.

5 The Belfry

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It only took 75-plus years but Batman finally smartened up and relocated downtown. You’d think the so-called “world’s greatest detective” would have set up a crime-fighting outpost in the heart of Gotham City years ago, but we have DC’s recent Rebirth to thank for finally making the big move. Although it seems to lack the surreal charm of the Batcave’s decidedly bizarre décor, the Belfry does make oodles of practical sense for a crimefighter of Batman’s stature. Plus, the dude’s rich, so he can afford to live downtown.

Outfitted with state-of-the-art computers, the Mud Room training facility and a vast arsenal of cutting edge Bat-gadgetry, the Belfry boasts all of the functionality of the old Batcave without the giant penny. Did we mention it’s downtown, where pretty much all of the crime in Gotham happens? Because we hear that commute from Wayne Manor can be a real killer. Just ask Tim Drake’s old man in “Identity Crisis”.

Location! Location! Location! How many lives could’ve been saved, Bruce? How many?

4 Avengers Mansion

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Arguably one of the most iconic houses in all of comics, Avengers Mansion has been the home to Earth’s Mightiest Heroes ever since Tony Stark handed over the keys way back in “Avengers” #2. Located at 890 Fifth Avenue, the mansion was originally Tony Stark’s family home, until he passed it on to the Avengers after taking on his Iron Man identity. Like virtually every other superhero lair, Avengers Mansion has been destroyed a few times over the course of its history.

The most recent structure served for a time as the home base of the Avengers Unity Squad, until they abandoned it. Currently, the repurposed mansion acts as an interdimensional theme hotel for tourists from across the multiverse.

Charming Heritage Building: Don’t let its stunning Beaux-Arts façade fool you. Over the years, the Avengers Mansion has enjoyed numerous security upgrades, making it one of the safest places in the Big Apple. Unless, of course, your name happens to be Gilgamesh, the Forgotten One.

3 Hall of Justice

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Undoubtedly best remembered as the headquarters of the animated Super Friends, the Hall of Justice remains one of the most distinctive superhero lairs of all time. Its unique art deco design evokes a modern, streamlined sensibility totally in keeping with the visual tone of the cartoon. Originally drawn by background supervisor Al Gmuer, the Hall’s signature look was inspired by Cincinnati’s Union Terminal. For years, aside from a few half-hearted attempts to tie the Super Friends cartoon to established DC continuity, the Hall of Justice remained confined to syndicated reruns and never made its way into the DCU proper.

It isn’t until the JLA’s first Watchtower is destroyed that the Hall makes its in-continuity debut, as a companion to the rebuilt Watchtower Satellite. Hopefully, with an upcoming appearance in this week’s Arrowverse television crossover event, the Hall of Justice returns to its rightful place as a majestic gathering place of world-class heroes.

Nostalgic Throwback: Art deco lines meet ‘70s pop culture cheese. What’s not to like?

2 The Fortress of Solitude

A diagram of Superman's Fortress Of Solitude from DC Comics

Even if you’ve never read a comic book in your life, chances are you’ve heard of Superman’s Fortress of Solitude. Arguably the most iconic entry on our list, Superman’s home away from home is located in the high Arctic, hundreds of miles away from prying eyes. Initially a refuge to which the Last Son of Krypton could get away from the constant din provided by his super senses and reconnect with his alien heritage, the old Fortress of Solitude hasn’t really been the most solitary places over the course of its existence.

It seems everybody and their uncle has at one time set foot over its vaunted threshold. Just check out the image above: How many JLAers are ambling about there anyways? And that’s not to mention the numerous times it’s been compromised by Superman’s foes. Despite its startling lack of security, the Fortress of Solitude remains a valuable item of Superman lore, registering in the popular consciousness with a potency rivalled only by our final entry.

Discreet Location: With polar bears and Arctic terns as your only neighbors, your privacy – not to mention hypothermia – is all but guaranteed!

1 The Batcave

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Although he recently unveiled a new state-of-the-art secret lair located in the heart of Gotham, Batman hasn’t totally abandoned his original digs beneath Wayne Manor. True, the new Belfry cuts down on Batman’s commute, as already mentioned, but what the old Batcave lacks in location, it more than makes up for in space and overall ambience. A swanky downtown location is cool and all, but condo living ain’t always what it’s cracked up to be.

Where does a billionaire masked vigilante park his Batsub, for example? And what about Batman’s notorious trophy collection? There’s no way he fits a giant dinosaur in the Belfry. It would clash with the established décor, for starters. The Belfry may make all kinds of practical sense but the Batcave is so intrinsically tied to Batman’s superhero persona, we can’t imagine it’ll ever permanently be replaced by a patch of prime, downtown real estate.

Covered Parking: One of the coolest things about the Batcave isn’t the incessant underground drafts but the massive vehicle bay, where Batman can store his extensive fleet of Bat-vehicles without ever worrying about parking.

Where do your favorite heroes hang their capes? Let us know in the Comments!