There are dimensions beyond which are known to man.
And there's one MCU superhero who specializes in journeying into these twilight zones. In Doctor Strange in the Multiverse of Madness, Marvel Studios dives headlong into the psychedelic reality warps of Steve Ditko, aiming for the otherworldly terrors of H.P. Lovecraft. Involving extraterrestrial landscapes that the Avengers are not accustomed to, Doctor Strange will need a group of new guardians that will protect Earth from the portal that the Scarlet Witch ripped wide open for otherworldly terrors to invade our planet. According to insiders, Dr. Strange will end up forming the Illuminati, a secret organization of highly intelligent and powerful individuals at the end of Multiverse of Madness. This mysterious collective will include Reed Richards and Professor X of the X-Men, being planned to make his debut in this movie. Please keep in mind that this intel is from private conversations that transpired before pre-production so any changes that have happened since are unknown. From this information, though, Professor X will make his first MCU appearance in Multiverse of Madness. Who else is being developed for the Illuminati?
Black Bolt, Namor, and Black Panther will apparently be joining this group of eggheads. And the magic has only begun. There has been talk of Scarlet Witch reviving Black Widow after wrestling her soul away as she puts the hurt on the Red Skull. Whether that happens in Multiverse of Madness remains to be seen but it's being plotted. According to multiple sources, Multiverse of Madness will be followed by Triumph and Torment in which Doctor Strange goes to Hell with Doctor Doom to rescue his mother from Mephisto.