Here on the East Coast, there's only about an hour left in June 14, also known as "Mutliverse Day" to DC Comics fans.
Multiverse day is the anniversary of the day Barry Allen discovered Earth-2 and, eventually, the larger DC multiverse as a result, in The Flash #123.
As Coliseum of Comics pointed out this morning on Twitter, this isn't a matter of "oh, the comic came out that day." No, in-story, a newspaper gives the date as June 14, 1961, making this canonically the 56th anniversary of the discovery of the DC multiverse.
There's something interesting, then, that Dark Days: The Forge #1 came out today, ostensibly ushering in a concept DC is billing as "the dark multiverse."
In DC comics, there are multiple universes, each of which takes up the same physical space but are separated by "vibrational frequencies." Speedsters can travel to alternate universes by vibrating at super speed and changing their own frequency.
That's how Barry Allen accidentally found Earth-2.
Earth-2 is an alternate Earth occupied by DC superheroes of the '30s and '40s, including the original versions of characters like Green Lantern, The Flash, and The Atom, while the versions of those characters (and other DC heroes) created in the late '50s and after lived on Earth-1.