Myriad Tower

There are at least a thousand active superheroes in the world. More than that counting sidekicks, retired superheroes, one shot wonders, and various people who think they're automatically superheroes because they have powers without realizing that's something that applies to about .5% of people in the world and climbing. (Sort of. If you take into account the ones who have potential but their powers never activated.)
Of all of those actual heroes, all of them will go through Myriad Tower at least once in their lives. It's a hub for all the different folk who go out there in costumes and attempt to save the day.
It's set up as its own sovereign territory, to avoid any one country being able to say "you guys are on my turf so you have to follow my rules or else." No one wants that. Well, some people do, but they're usually surrounded by smarter people who realize that if it applies to them then it applies to everyone else and any advantage wouldn't last long.
Myriad Tower is a massive skyscraper that did get the brief title of tallest in the world. In terms of functioning levels and not counting the antennae that stick out of most of the other ones to give them the title, this one has a lot of space inside. There's a little bit of tech involved to cram more floor space into less actually physical space. It's kind of fun.
Most of the really popular heroes have some kind of suite in the building, a place to stay, a home base, a space to meet with other heroes, and access to the gym. Seriously, the gym is amazing. Perfect for training up.
There are of course other towers in the world that also house superheroes, but Myriad Tower is the big one.

Type

Skyscraper