While the Quantum Realm is still a deeply mysterious space in the world of the MCU, Marvel comics have actually explored this dimension - also known as the Microverse - in great detail. Characters like the Hulk and Doctor Doom have had numerous adventures inside the Quantum Realm, but few characters have spent longer inside than The Wasp, aka Janet van Dyne, who became a freedom fighter in the Microverse during a period in which she had been assumed dead by her Avengers allies.
First appearing in Captain America Comics #26, the Quantum Realm is often mistakenly thought of as a smaller universe that can be accessed by physically shrinking. In fact, it's actually a parallel dimension usually reached by the dramatic compression of matter, hence why so many Marvel heroes have found themselves there in accidents relating to size-altering Pym Particles. The structure of the Quantum Realm has changed a great deal over the course of Marvel comics history, with multiple dimensions merging together within its constraints, creating a place that's both physically and politically unstable.
The Wasp found herself in the Quantum Realm following the events of Secret Invasion. Having been given new size-increasing powers by a Skrull disguised as her husband Hank Pym, Janet was converted into a weapon by the invading Skrull forces. Generating a deadly explosive force, Janet was seemingly killed by Thor in an attempt to save Earth, but she was actually able to shrink down so rapidly that she made the jump to the Quantum Realm, leaving behind no physical evidence that she had survived the thunder god's regretful attack.
Janet's true fate was recounted in 2010's Avengers #31, where it was revealed that her two-year absence from Marvel comics had been spent as a fugitive in the Quantum Realm, where she had made an enemy of the centaur-like warlord Lord Gouzar. Following a lead given to her by the Microverse pirate Ritch-Ellatali, the Wasp fights off Gouzar's mercenaries and is able to boost the reach of her Avengers Identicard, sending an emergency signal to the Avengers back on Earth.
The Avengers head to the Quantum Realm to rescue Janet but are quickly imprisoned, freed only with the help of a recently rehabilitated Wonder Man. After saving Iron Man from Gouzar, the Wasp is able to return to Earth, where the assembled Avengers finally defeat Lord Gouzar, who grows significantly in power and size when outside the Quantum Realm. As the finale of Bendis' run on the Avengers titles, it's a fittingly huge victory for the Wasp, a founding Avenger who has also acted as the team's chairperson - the implied scale of Lord Gouzar's control suggests that the Wasp may even have freed the entire Microverse from his control.
With the MCU's Janet van Dyne having escaped from the Quantum Realm in 2018's Ant-Man and the Wasp, it's possible that future movies will take advantage of this version of the setting, which is close to Star Wars planet Tatooine in appearance. Whether the movies pick it up or not, Janet's ability to survive in the Quantum Realm for so long shows why no-one should be underestimating The Wasp.
