Subscribe from any calendar software that supports ICAL by either copying or downloading the following URLs:

Google Calendar

Instructions from the Google Calendar docs:

1. Open Google Calendar
2. On the left, next to "Other calendars," click Add Add other calendars and then From URL.
3. Enter the calendar's address.
4. Click Add calendar. The calendar appears on the left, under "Other calendars."

It may take up to 12 hours for calendar changes to propagate.