Justine,
Thanks for getting in touch! Unfortunately, it’s not currently possible to have a publicly accessible hidden event. However, you can set an event as ‘Private’ (instead of Protected) which will completely hide the event for users that are not logged in. If logged out users try to access the event, they will just get a 404 error.
The other option would be to create a new Event category (ex: Hidden Events) and then use CSS or PHP to hide all events in that Category.
I hope that helps to get you started in the right direction, but let me know if you have further questions. Thanks! 🙂
-Casey-