Go to the MyActions drop-down menu and click
MyURLs.
On the URLs page, select the calendar, or multiple calendars, from the list of published calendars and then
press the
Widget API button. You will get a name for your calendar in the URL field. Click the
copy URL button to copy that URL
onto your clipboard.
You can select more than 1 published calendar, and you will get a comma separated list of calendar names.