This article contains spoilers for X-Men #1.
The X-Men's new headquarters is their coolest yet. It's a fact that all the best superheroes have a cool headquarters. Batman has his Batcave, Superman has the Fortress of Solitude, and Harley Quinn annoyed Green Arrow by suggesting he should really call his base of operations "the Quiver." The teams even usually go one better, with the Justice League associated with the Hall of Justice or the orbital satellite called the Watchtower. The Avengers have currently upgraded from Avengers Mansion to their most bizarre headquarters of all; they're living inside the body of a Celestial, an ancient cosmic being.
The X-Men have had some pretty outstanding bases. They're typically associated with the X-Mansion, which - as Xavier's School for Gifted Youngsters - can be found in Westchester, New York, and includes a mammoth subterranean base and hidden facilities for launching their Blackbird Jets. But they've also been based on islands such as Utopia, an artificial construct they created offshore of San Francisco, and Cyclops once chose the Weapon X facility as his headquarters because he rightly guessed it was the last place Wolverine would ever look for him (they were feuding at the time, and Scott Summers was Public Enemy Number One).
Recently, Cyclops and Jean Grey have reformed the X-Men, and in X-Men #1 by Gerry Duggan and Pepe Larraz they unveil their new base to the world. The White Queen used mutant funds to acquire property at the southwest corner of the 86th Street Central Park Transverse, and when residents woke up the next morning they were shocked to find the landscape had completely changed. Existing structures had been quietly replaced, and the X-Men had grown a literal treehouse there, which they're calling "Seneca Gardens" in honor of New York's history. As Cyclops observes in an unwise spontaneous interview with journalist Ben Urich, the age of Krakoa is allowing him an opportunity to express the creative instincts he suppressed for years as he fought to protect a world that hates and fears him.
The Treehouse is undeniably the coolest base superheroes have ever established in New York. As Ben Urich notes, most superhero headquarters are ominous and imposing - think of the Inhumans' New Attilan floating over the city for a time, the Sentry's Watchtower, or the always-ominous technology associated with the Baxter Building. But the X-Men... have a Treehouse. "If the mutants have some grand design to take over the planet," Urich reflects, "they're doing it with kindness, and we can always use more of that." Inside, the Treehouse is as different from the X-Mansion as anyone could imagine, because it doesn't have the typical training facilities. There's no Danger Room as the X-Men don't need it anymore. There's an operations hub, a hangar level for their new jet, a habitat level, and a medical bay - and, of course, if things get bad the X-Men can hop through a Krakoan portal to instantly get to mutant healers.
More than anything else, the Treehouse is simple. It's a demonstration of mutant biotechnology, but it's not ostentatious, and it doesn't dominate the area in the way most visible superhero bases do. It serves its purpose, it has everything the X-Men need, and it stands as a testimony to mutant science and nature. It's also seriously cool.