Opening a calendar in Outlook is straight forward. Always ensure that you have the published URL’s. If you opening a published calendar from Exchange, you should have two links. One is an .ICS file and the other is a .Html. The Html is used for viewing the published calendar via a web browser. The .ics is used for opening in Outlook.
Here is an example of the above mention links:
In order to open up the calendar in Outlook, go to your calendar:
Select “Open Calendar“. This should be located on the top ribbon.
Drop down the list from Open Calendar and select “from Internet”
Enter the URL which contains .ics in the end. Depending on the environment which publishes the link. You may need to ensure that in the beginning of the link, it has HTTPS instead of just HTTP. The reason for this is that it is more secured.
This will open up the second calendar published via internet.