The Nonexistent Knight is a good story. Calvino plays with words, and does a lot of things that I would call "meta," but he makes his story readable, using humor, suspense, and lots of good detail along with a kind of word play, irony, and self-referential stuff.
Agilulf is a nonexistent knight -- a suit of white armor with nothing visible inside. Agilulf walks around Charlemagne's war camp, enforcing the formal rules that only he knows, and doing highly chivalrous acts. Such a knight, you might say, is nonexistent. Right.
Agilulf gets into a shipwreck, sinks to the sea floor, and walks to the destination port, his armor conveniently coated with protective goo. Such a knight, you might say, is nonexistent. Right.
Somehow, Calvino fleshes this character out, despite his lack of flesh. He has ideals, desires, and thoughts. He doesn't eat, but plays with food that's served to him. Calvino does it all with subtlety and creates a plot that gets the reader interested.
The narrator is a nun. She gets engrossed in the process of writing. She draws maps and finds out where the characters are by looking at her own maps. She speculates in odd ways. But she's somehow likeable and the final revelation about her is a nice surprise. This meta stuff doesn't spoil a good story, just adds to the amusing nature of the tale.
Chalemagne gives Aigilulf Gurduloo as his squire. The nonexistent knight is the master of his opposite: Gurduloo (who also goes by many other names) is entirely engulfed in physical reality. In the shipwreck that his master walks away from, he can't tell if he's in the sea or the sea is in him. Somehow this saves him. When he eats soup, he's in the soup and says "All is soup!" Somehow his odd existence is captivating.
In one scene, Charlemagne sat down to a banquet before the proper time and "began to pick at bread or cheese or olives or peppers. ... The courses were the usual ones in a military mess: stuffed turkey roasted on the spit, braised oxen, suckling pig, eels, gold fish." When Agilulf ate, he asked for "fresh crockery and cutlery, plates big and small, porringers, glasses of every size and shape, innumerable forks and spoons and knives that had to be well sharpened." Then he played with the food. Another scene involves tribute from peasants to the Knights of the Grail: "goats' cheeses, baskets of carrots, sacks of millet and young lambs."
Do we readers care that peppers, turkey, forks, and carrots are anachronisms? No, it's the vivid details that work here. Nothing about the writing can be critiqued for consistency. It's a game. If you don't get it, the joke's on you, I think.
Note: Calvino's book If on a winter night a traveler made it onto the L.A.Times book blog list of postmodern novels, where there's also a list of postmodern characteristics that might be relevant here. See this:
61 essential postmodern reads: an annotated list