The Batman/Fortnite crossover we knew was coming thanks to a datamined leak is live now, on what is apparently Batman Day. It'll continue for the next two weeks (or what some of us call a "fortnight") during which Tilted Towers will be transformed into Gotham City.
There's also a Caped Crusader Pack of Bat-themed weapons and cosmetics, which is available until October 6. It's got both a comic-style Batsuit and one that's more like the armor Christian Bale wears. There's a Catwoman outfit in the store too.
As the latest patch notes point out, in Gotham City everyone has unlimited glider redeploy for maximum swooping. There's a Batman grapnel gun you can score as loot, which works as you'd expect a grapnel to with the advantage that it also deploys a Bat-cape glider at the apex of your grapnel launch. Explosive Batarangs are also available as loot, which detonate if they hit other players but act as proximity mines if they hit the environment.
Various heroic Challenges are available until October 1, handing out rewards from a Welcome to Gotham City challenge bundle that includes a Catwing Glider.
It's all in service of Batman's 80th Anniversary. Happy birthday, old man.