I'm wondering how do you use PHP to make it look like there are directories that don't even exist.

I can't point to specific websites but I've worked on existing code (didn't have a chance to look at the code that did this function) where there are pages that look like www.mydomain.com/products/inside/Model# but only the products directory existed. There was not inside directory.

How do you do this? Does it require special configuration via apache or can it be done in only php?