The issue opens with "What Lurks Beneath The Mask", with Doctor Strange on the run from the minions of the Dormammu-powered Baron Mordo, looking for the secret of "Eternity" to save the stricken Ancient One. Especially good in the opening pages are the hints of a whole magic subculture with various odd mystics thoughout the world on both sides of the battle, and a quick hint about a never followed up on past Doctor Strange adventure. Anyway, in his haste Doc misinterprets a clue from a crazy old mystic whose memory the Ancient One had once erased and winds up in a strange realm with a demon who tries to switch bodies with him. There's a great scene where Doc uses his Cloak of Levitation to battle the demon inhabiting his body. Great little side-story in the middle of a longer epic.
In "When Meet The Mystic Minds" Doctor Strange decides that he has to find out the secret of Eternity directly from the mind of the Ancient One, which leads to an excellent sequence of increasingly bizarre visuals as he attempts to reach his mentor. The closing scene, with Doc atop a mountain walking into an enlarged amulet just ahead of Mordo's arrival, that's how you do a cliffhanger.
"If Eternity Should Fail" opens with one of the best renditions of the mystic realm in Ditko's work, probably the panel you'd put in the dictionary if you needed one image to define "Ditkoesque". And that's just the beginning, as we next get introduced to Eternity, the living embodiment of a universe, who offers the type of enigmatic advice you'd expect from someone who looks like that. Returning to his own realm, he finds the Ancient One has been captured by Mordo and goes to confront his foes, who also have the unnamed woman who helped him in Dormammu's realm held captive.
Seriously, this is 30 incredible pages of comics. If you've never read them you owe it to yourself to check out one of the multiple versions of this run that should be readily available now. Added bonus in this version, they got some of the new guys to do some pin-ups in the back, and this one includes a great image by P. Craig Russell titled "Dr. Strange gets lost on his way to the Surrealist's Convention", which is even weirder than what you're imagining.
The 7-page "Valley Of Eternity" was published in Charlton's TALES OF THE MYSTERIOUS TRAVELER #11 [1959]. This is probably the Charlton series of the era most associated with Ditko, thanks to his iconic renditions of the host in his trenchcoat and fedora, often floating as a giant in the background. He sticks to human size in this one, as he presents the story of four very different men whose paths cross in a hidden valley in India, where they find the promise of a secret that could change them and the world. 
