Finding the import URL for your Google Calendar is not as straightforward as it sounds. Here are the correct steps:
First, in the 'My Calendars' section, click the menu (dots) next to the calendar you are wanting to import, then click 'Settings and sharing'.
Next, scroll down to the 'Integrate calendar' section and look for '... address in iCal format'.
You may use the 'Public' or 'Secret' address. Both will work.
To get those events imported follow the instructions in this article.
That's it!