Sandro loves Anna but Anna is unhappy and causes herself to disappear. Claudia is Anna's friend and joins Sandro in what often seems an unfocused effort to find Anna. Now Sandro makes love to Anna and Anna mostly accepts this but feels guilty about Anna and is often languid in her responses. The women can talk about feelings to each other, but since Anna leaves the film so early we don't see much of this quality; the men can't talk feelingfully to each other, nor to the women. In one scene, Claudia and Sandro are in a small village; while Sandro goes looking for Anna is a (literally) hole-in-the-wall hotel, Claudia waits for him outside that wall, as the men of the town slowly circle around her, wordlessly staring.
This is Antonioni's L'Aventura of 1960. Any extraneous plot or info-providing dialogue has been cut, or, rather, was never there. The easiest thing to say about this film is that it is about ineffability.
But Sandro is an architect and the father of the unhappy Anna is what we'd today call a developer. The landscape of the film is covered with architectural forms. Very few scenes are not framed by the shapes of the built environment. Sandro and Claudia, wandering around what I suppose is Sicily, move in and out of soft- and off-white lines and shadows cast by buildings. They are caught between the old forms and the new. Since Sandro's apartment (which we see briefly at the beginning) is gorgeously modern, in a southern clime kind of way, we assume that Sandro is in favor of the New. But Anna has been lost into the Old. They are in different universes but it doesn't seem to bother Sandro at all. That's perhaps the oddest of the many odd feelings one has watching this film.