Best php navigation method with sub directories in mind : I'm looking for the best method for creating a single navigation menu and including it with php. I know how to do just about everything I need, the problem I'm running into is the sub directories. 

For example:
Nav.php is in the root directory. 
`Index.php` is also in the root directory. 
Now I want to go to a page about cats, located at `about/cats.php`. 

When I want to go from `about/cats.php` to `blog/kittens.php` how would I structure the links? 

`<a href="about/cats.php">cats</a>` would take me to about/cats just fine from the root directory. But if I'm on the `blog/kittens.php` page, I'd get a link like `about/blog/kittens.php`. 

It's not something that needs massive/dynamic arrays or anything, I've just had a hard time wrapping my head around the cleanest way to do this. 

What's the best method to keep one navigation file(if possible) but still have correct links even if I'm 2 or 4 levels from the root? I've seen others use sql databases (if that's the best way I don't mind), but I feel like that's too complicated and I'm just missing a much easier method. 