Mapping of URL directly to a template file you describe (mapping URL to a file) is quite rare technique in WordPress, sometimes called static pages.
It is rare because in general that's not how WordPress works. It works by mapping URL to query variables to WP_Query to template hierarchy to template file. Going from URL to a file skips a lot of mandatory steps.
The low key implementation would be to create a page and make your file a custom page template for it.
The more direct implementation is also possible, but you would have to both build a custom rewrite rule and implement processing it from scratch.