Hook any php file into the wordpress api

Say I just have a dumb .php file sitting on my WP server and I wanted it to access WP info through the API, how would I go about doing that? For example if I wanted to call

 bloginfo('url');

As I have scored myself a downvote (with no explanation) I will expound upon why I am interested in this. Sure I can access WP API from all the built-in pages. But let’s say I have a page that has little to do with WP. Seems like a lot of overhead to create say a custom template page and then hook it into an actual post, all so that I can have access to a few WP API calls.

I ended up using something like this:

require $_SERVER['DOCUMENT_ROOT'].'/wp-blog-header.php';