OK, Stackers, here's another nugget from my imperfect memory of forgotten future and sci-fi paperbacks.
Read, in paperback, somewhere between 1963 and 1966.
Humanity seems to be in a subterranean location with many levels, perhaps forced to live there, perhaps due to yeast plagues or wars. Yeasts seem to be a recurring motif in the novel.
Written from the viewpoint of a single, relatively young male, who may be a member or agent of a secret society. He is compelled to take a journey through some of the levels. He had survived a yeast plague because his mother was a prolific home baker. A level he traverses has an inland beach and swimmable sea, with an artificial sun and horizon, he swims out to the fuzzy edge and finds a metal wall. On the beach (sorry) he converses with a man and meets a dog he sees (with psi power-like x-ray vision) has an internal growth, he recognizes it as a second brain. The dog becomes his guide for a while, they communicate empathically.
He meets a woman, they greet each other with the modern Wicca-like phrase of "Blessed be", another motif. There is mention of the Athame (a ceremonial knife). He has visions of acting as a Cretan bull-leaper, this vision is an analog for other psi powers.
The novel ends optimistically for the hero and humanity, memories are restored, he is more fully received into the society.
NOT "A Boy and His Dog" (Ellison), though I appreciate the similarities.
I commend my soul, and these snippets to the greater group memory: anybody, anything?