This weekend I was accidentally deleted an iCloud Calendar. And of course, thanks to Apple’s quick sync the Calendar disappeared from all my devices in no-time :(

Here’s how I managed to restore the Calendar:

1. In Finder, hold the ⌥ option key to go to the otherwise hidden Library folder under the Go menu.
2. Navigate to Calendars.
3. Find out which *.caldav folders is of your iCloud Account by checking their Info.plist.
4. In that folder, take note of all remaining *.calendar folders.
5. Enter Time Machine.
6. Browse back in time until you see a new *.calendar folder appear.
7. Restore the folder to a temporary folder like your Desktop.
8. Use this NodeJS script to prepare the *.ics files. It generates a new UID and removes X-* tags so that iCloud will treat them as new events. If you don’t, the events will import at first, but then automatically get deleted again after some time.
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   $ npm install $ node ics.js ~/Desktop/ABC.calendar/Events ~/Desktop/output

9. Open Calendar and create a new iCloud or local Calendar.

10. Select all *.ics files and drag them on the new Calendar in the sidebar. Don’t drop them on the Dock item – it will open a dialog for each event.

You’re welcome.