Never say I don't give this community some little gems once in a while. I came up with the concept of creating a directory structure using nothing but valid HTML5 and CSS3. It uses an unknown "checkbox hack" concept which some HTML5/CSS3 purists consider to be beyond the semantics of the language. But I say if it's supported by all major browsers and it works, then why not!
Note: I used >KaFu's idea for the current level and next level, but the rest I came up with myself, albeit I have use