How do I create a configuration sync folder? I've inherited a Drupal 8 site but it has no config_HASH folder with it which means that the majority of admin paths throw an exception.

How do I generate a new configuration folder based on the current site?
To generate a new config folder do the following:

In settings.php add the following line:

$config_directories['sync'] = 'dest/to/config-sync';


This is relative to your docroot or index.php file.  My permission were set in a way that drupal could create this directory but you may have to create your own.  Next you will want to populate your sync directory with active config. Run  

drush cex -y


Now your active config can be version controlled and deployed to your other environments. Remember to make a database backup first before importing config.