Indexing directories of files ("Filepath on server")
You can also have directories of files on your server indexed periodically, using the type "Filepath on server".

Indexing configuration for a directory
Again, the options are either easy to understand or your can read more about them in the Context Sensitive Help.
Location: The Indexed Search configuration should be located on a not- in-menu page, just like the "External URL" type required. Same reasons; results are bound to a page in the page tree.
The process of indexing a directory of files is the same as for the external URL: For each directory a) all files are indexed and b) all sub-directories added to the crawler queue for later processing. This is shown in the crawler log:

Crawler log entries for directories
When processing is done the result is shown in the Web > Info, "Indexed search":

Verifying the list of indexed directories