Have you ever heard of Gabriel's Horn? It's a mathematical shape, a deceptively simple "solid of revolution" that will melt your brain. It's also one of my very favorite things of all time. Oh my yes, you'll love this:
https://badastronomy.beehiiv.com/p/a-geometric-shape-that-will-destroy-your-brain
@badastro ok I may be very stupid but isn't the inside only finite in volume if the particle size has a fixed definition relative to the surface area? Because you can have infinitely small particles crammed into the gap between the surface and your axis, then the fact those two never meet means you can still cram volume in there infinitely? Or is there some bit I'm missing where it stops mathing?