Superhero headquarters? Superman has his Fortress of Solitude, and Batman has the Batcave. The Fantastic Four have their Baxter Building in downton Manhattan.
For my money, though, the SECOND best one was the Justice League Satellite -- a massive satellite in geosynchronous orbit some 22,300 miles above the Earth.
Originally, the Justice League of America operated out of the Secret Sanctuary -- a six-story base built inside a cave near the small town of Happy Harbor, Rhode Island. (I know: What th'...?) Happy Harbor was the home of Lucas "Snapper" Carr, a beatnik teenager who helped the League defeat its first villain (the alien Starro the Conqueror). He became the League's "mascot". (His nickname, Snapper, comes from his habit of snapping his fingers all the time.) Eventually, Snapper becomes ashamed of being the League "mascot" and betrays the location of the Secret Sanctuary to the Joker. (This occurs in Justice League of America #77 [December 1969].) Having committed no crime, he is spared prison -- but never again associates with the Justice League.
Within two months, the Justice League moved into their new satellite. (This occurs in Justice League of America #78 [February 1970].) It was your basic ball surrounded by a ring section. Oddly, there were four rockets in the ring section, although their purpose was unclear. Hundreds of thousands of invisible teleportation chambers were placed all over the world, allowing League members to get to the satellite easily. Sadly, anyone could use the teleporters. The villain Mark Shaw, variously known as the Manhunter, Privateer, and Star-Tsar, managed to use one to gain access to the satellite. So did the villain Dr. Light, who found Elongated Man's wife, Sue Dibney, alone there. He raped her, which set in motion a series of events that destroyed the Justice League.
The look of the JLA Satellite was initially a smooth one, fitting the sci fi design ethics of the 1970s. But in the 1980s, a more "realistic" looking satellite was unveiled. It was the same design, just with a lot more surface texture.
The JLA Satellite is supposed to survive into the 30th century, abandoned. There it explodes, and three of the items in its trophy room -- the Wheel, Bell, and Jar that summor the Demons Three (Abnegazar, Rath, and Ghast) -- are hurled back in time where the evil sorceror Felix Faust finds them and uses them to regain vast power.
However, DC Comics abandoned this history without explanation. In Justice League of America #230 (September 1984), the Green Martians attack Earth and severely damage the satellite, rendering most of it uninhabitable. Aquaman disbands the Justice League in Justice League of America Annual #2 (October 1984). The hero Red Tornado, his robotic body taken over by a supervillain, self-destructs aboard the satellite in Justice League of America Annual #3 (August 1985), and that's the end of it.
The Justice League briefly used Overmaster's "escape pod" (really, a large starship), the Refuge, as their space-born HQ in the early 1990s. The Blue Beetle had destroyed the Overmaster's ship in Justice League Europe #66 (September 1992), but the escape pod jettisoned and stayed in orbit. Wonder Woman claimed it as the League's orbiting headquarters. The Refuge was launched into space by Lord Havoc in Justice League of America #110 (April 1996), and two issues later it was captured by the galactic mercenary Flicker. In Justice League of America #113 (August 1996), it returned to Earth. The League continued to use the Refuge, but it also established an land-based headquarters at Captain Atom's Mt. Thunder, Nevada, headquarters. The Refuge crashed to Earth and is destroyed in Justice League of America #1 (October 2006).
The Justice League then went international, with league chapters in every major country of the world, and most major U.S. cities. These various incarnations of the League each had their own land-based headquarters (none of them secret).
FINALLY, in JLA #4 (April 1997), a new headquarters was built on the Moon. Called the Watchtower, it was built of the most advanced Kryptonian, Martian, Thanagarian, Oan, New Genesis, and Earth technologies available. It was copmpletely destroyed in JLA #120 (December 2005) by the Superboy from Earth Prime, who was driven mad by his realization that he was not the "only" Superboy.
TWO new headquarters debuted in Justice League of America (vol 2) #7 (May 2007). The new satellite is MASSIVE, and consists of a long cylindrical lower core, a bulky cylindrical central core, a somewhat conical upper core, and a tower with spine projecting out the back. Thrusting outward from the lower core is a golden spike about 200 feet long which contains the power plant, mechanical systems, computer cores, and some offensive and defensive weapons. The lower core itself is about 23 stories high, and has four projecting ribs which taper as toward the bottom and which hold the power spike. The center section is a about 10 stories high, and slightly tapers toward the top. It is three times the diameter of the lower core. The upper core is eight stories high, and has upright golden flat segments set at eight equidistant places around the core. These provide both power and defensive shielding. The tower is 16 stories high, consisting for a two-story conical base tapered at the top and a 12-story cylindrical tower above. A flat spine projects backward from the tower, to connect with the "rear" of the satellite. The tower and spine are topped with various long antennae. Attached to the station are two partial rings, open at the front. The lower ring is about eight stories high, and is connected to the "rear" of the satellite at the upper end of the lower core. The second ring is also about eight stories high, although its diamete is slightly less than that of the lower ring. It, too, is connected to the rear of the satellite, this time at the back of the upper core. The new satellite has both offensive and defensive weaponry, and is protected and maintained by a series of space-going drones. It was designed by Wonder Woman and the Green Lantern known as John Stewart, and aid for by Bruce Wayne.
Jim Lee designed the new satellite based on the satellite HQ seen in the cartoon series Justice League Unlimited, the old JLA satellite, and some new designs. Five different designs were rejected before a sixth, composite design was approved.
At the same time, a Hall of Justice was constructed in Washington, D.C. The site is that formerly used by the Justice Society of America and All-Star Squadron. Again, the Hall was designed by John Stewart and Wonder Woman, and financed by Batman. Itis 12 stories high, and its blast-resistant walls are reinforced with titanium plates. It has the diplomatic status of a foreign embassy, and is considered not part of the United States. The public area of the Hall of Justice serves as a museum about super-heroes and, in particular, the Justice League. The museum contains a gift shop and various trophies of the League, including now-useless weapons used by super-villains. But it also functions as a headquarters for the JLA, and contains a meeting room, combat training room, hightechnology clean lab, robotics laboratory, a radiation lab, storage rooms, a teleporter that connects to the Justice League Satellite. Three stories exist below ground. At the bottom of level is the morgue, where the bodies of slain villains rest to prevent enemies from harvesting superhumans parts for re-use.
The Hall of Justice originally appeared in the Super Friends animated TV series on September 8, 1973. It was designed by Al Gmuer, a backgrounds supervisor for Hanna-Barbera. (Gmuer modeled it on the Art Deco Union Terminal in Cincinnati, Ohio.) Elements from this cartoon show were integrated into the mainsteam DC Universe following the "Flashpoint" retcon of the entire DC Universe in 2011. It first appeared in Justice League of America (Volume 2) #7 (May 2007).
The Hall of Justice was appropriated by the United Nations as the headquarters for the Justice League International in Justice League International (Volume 3) #1 (November 2011). It was bombed and severely damaged in Justice League International Annual (Volume 3) #1 (October 2012).