Here’s an inside-out thought: The air around us is a 3-manifold with 3-holes where solid objects are, and the 2-boundary is the ground. Or if you think of all the sky, it’s a spherical 3-shell (with one 3-hole, the Earth) floating in empty space.
I wish I could draw what I’m thinking of. Something like this.
From a child’s-eye view, “the air” is the complement of everything that’s “actually there” (solid or liquid things).
You could correct that child by bringing up outer space (another 2-boundary on the air), or the fact that air is made of particles as well.
But wouldn’t you rather be sitting in the middle of a field imagining yourself, the trees, the grass, the clouds, the birds, and the wood chips being cut out by a Photoshop lasso?