You don't have to imagine it, it is the Earth known as Earth-Prime, and Flash took a run there!
Here's some of the story of Earth-Prime!
The Flash -- Fact Or Fiction?
Backtracking a bit, it seemed like a normal day for Barry Allen...
...facing off against an alien creature who seemed to appear wherever he was, meeting the alien hunter who had trapped the creature, finding out the creature was the Nok, given a time limit in which to catch the creature, then facing some ordinary museum thieves...
...at least until the Nok showed up there, too!
With a quick super speed change, convinced him that he was the real thing. Barry stayed and read comics while Julie went out to get the parts needed to build a Cosmic Treadmill, which would allow Barry to speed back to his own Earth, which he did.
Julie Schwartz having an idea for a new story for the Flash back on his Earth).
The Day I Saved The Life Of The Flash
This time around, Cary Bates (who wrote the previous tale as his first outing as a Flash writer, soon after, becoming the regular writer for the Flash) was driving around Ohio (with just a little problem of driving too fast) when he found his way into a mysterious fog...
...which transported him all the way to another Earth, and to Central City, instead of his original destination of Athens, Ohio.
Cary went to the home of the Allens, and, with a little work, convinced Barry that he was who he said he was, putting the Flash on the trail of the Trickster.
Flash confronted Trickster, but was stopped by the new gimmick the Trickster had, that of a hypnotic yo-yo, which caused Flash to forget who he was facing.
So, Cary thought of a new robbery for Trickster, which the Trickster performed, then Flash showed up, and found a way to prevent James Jesse from making a clean getaway.
Thanking Cary for his help beating the Trickster, Cary used his "plotting power" to create the fog again, and drove home, knowing he'd have a new story for the Flash (not unlike how Julie Schwartz did).
Earth-Prime came back for a JLA/JSA team-up (where that Earth was named, and Cary returned there), as well as introducing two super-heroes of its own, Ultraa and Superboy!
But, Earth-Prime didn't fair so well during the Crisis On Infinite Earths....