A strange interlude in Don Quixote

Someone - I think it was a translator of the Divine Comedy (Palma) - remarked that all great works include some passage or section that is totally strange and, initially at least, apparently not in sync with the rest of the work (in the DC it was a section about Mantua) - and I think that's true and I think in Miguel de Cervantes's "Don Quixote" that section involves DQ's descent into the Cave of Montesino (?), a whole section, that, even in this episodic novel, feels like a divergence, and DQ, Sancho Panza, and a relative of someone they meet along the way who's pretty much identified only as "the cousin" and who serves as their Virgilian guide, travel off for a few days to visit this legendary cave, into which they lower DQ by rope so that he can explore the interior passages. The psychological interpretations are pretty obvious and heavy-handed, but what else does DQ's descent into darkness represent? He believes he was down there for 3 days (they say it was only an hour) and that he met a whole society of people who recognized him and prophesied his success - of course this is more of the mock-heroic tone of the novel, echoing Ulysses' descent in the Odyssey and Aeneis' as well I think - but in this case the visions are full of grandiosity and delusion - or are they? Is DQ actually seeing in some ways his future as a figure in world literature, is he actually envisioning the literary stature of Cervantes that he, DQ, will secure? Or is it some strange sense in which a character is able to foretell his own evolution and development - because surely DQ does learn and grow of the course of this long novel, his madness never abates but his discourse seems increasingly wise and, in the later chapters, his valor actually helps people out of predicaments (he stops the rioting at the wedding of Quiteria) rather than creates havoc for himself and others.