Quantum Realm

The Microverse (also known as the Quantum Realm) is a location that can only be reached by shrinking down to subatomic size.

It's a vast parallel dimension full of both magic and high technology.

The natives of the Microverse are the Micronauts, who struggle to free their dimension from the clutches of the tyrannical Baron Karza.

During a mission to defeat the Ten Ring in the 60s, Janet Van Dyne got accidentally trapped in the Microverse, where she spent most of life until she managed to escape in 2017.

Scott Lang and Darren Cross also entered the Microverse during their struggle after Scott foiled Darren's plans. Scott managed to defeat Darren by making him fuse with the subatomic particles there, turning him into a quantum anomaly. Scott managed, after much effort, to escape from the Microverse.