how to get calendar data out of an ICBU file without using Apple Calendar app

I have a 1.7 GB ICBU backup file made from Apple Calendar from which I need the data but which will not open with Apple Calendar app. using its Restore function. Further details: The file is in my Downloads folder; when I pick that file, the descriptive data shows the file as having 1.6GB. However, when I try to Restore it using Apple Calendar app., the calendar is blank. Is there a way to somehow access the data that should be contained in that 1.6GB file? If not in Apple Calendar app., in some other way (not using the Restore function in Apple Calendar app.) so that I can see the data so that I can hand "restore" it to the calendar app.?