Working Links:

iOS - Add to Calendar

Google Calendar URL

Unsuccessful attempts:

Google URL

Google URL /render

Google URL /calendar/r

Google External ICS webcal

Google External ICS webcal Encoded

Google External ICS https

Google External ICS https Encoded

Google External ICS http

Google External ICS http Encoded

google.com/calendar External ICS webcal Encoded

Download ICS

Google Calendar URL v2