Can't use backup migrate module, CIVI crm error is: "The website encountered an unexpected error. Please try again later."
To clear up the smaller issue - Drupal, like most modern web apps, will not have a directory corresponding to most of its URLs.  It will use redirects (defined in the webroot .htaccess file) to map URLs to a dynamically-generated page which doesn't exist on disk.

To speak to your primary issue - it sounds like you've got a MySQL view in your database.  CiviCRM doesn't typically create MySQL views, though there are some exceptions (I believe CiviCase might use them).  There are also sometimes reasons to create them manually - for instance, I created one for a client so CiviCRM could integrate with software that produces membership cards.

You have a view that references data that no longer exists.  It seems someone recently deleted a custom field group called "Files" with a custom group id of 8.  You have a MySQL view built in part from the table that holds that data.  The table is gone, so the view is broken.

Most likely, if the custom group is deleted, you no longer need the view, and it's safe to simply delete the view using PhpMyAdmin or similar.  However, it may be worth exploring whether that custom field group was deleted intentionally.