Stranger Things has become one of Netflix's biggest shows, with the series earning critical-acclaim and spawning a franchise of its own that has seen it expand to books, video games, and more. And now, with the highly-anticipated third season of Stranger Things set to kick off on July 4, a crossover event has started in the popular battle royale game Fortnite.

The full scope of the Stranger Things/Fortnite crossover is unknown at this point, but it will likely shift into full gear when the new season premieres on July 4. In the meantime, portals to the Upside Down - an alternate universe inhabited by monsters in the show - have started appearing at various locations on the Fortnite battle royale map.

These Stranger Things Upside Down portals seem to appear mostly inside buildings. Players are free to go through them, though they don't actually end up in the Upside Down when they do so. Instead they are simply teleported to a different Upside Down portal elsewhere on the map.

The Stranger Things/Fortnite crossover was first announced a few weeks ago, but further details on it are still unavailable at this time. If it's anything like the other crossover events in Fortnite, then it will likely feature some limited-time cosmetics for players to unlock, as well as a Stranger Things game mode and special challenges.

In the meantime, playing the Stranger Things content in Fortnite isn't the only way fans of the show can experience the world of Hawkins, Indiana in video game form. Releasing tomorrow alongside the show is Stranger Things 3: The Game, which is a retro-style beat 'em up.

With the success of the Avengers and John Wick crossover events, it's no surprise that Fortnite is crossing over with other popular franchises as well. Just how extensive this Stranger Things crossover event is remains to be seen, but more should come to light in the coming days.

Fortnite is out now in early access for Android, iOS, PC, PS4, Switch, and Xbox One.