Outlook Classic
1. Open Outlook. In the bottom left corner, or on the side menu, click the Calendar icon.
2. Right click My Calendars in the left pane, select Add Calendar, and then click From Room List.
3. Search for the calendar you're looking for. Double click the calendar in the search result and click OK button. In this example "IT Vacation Calendar" is being added.
The calendar will now be shown under "My Calendars" on the left side in Outlook.
New Outlook
Select Calendar View from the left hand panel
Select the "Add Calendar" button:
From the pop-up window select "Add From Directory" and then select your own address from the dropdown. Search in the bar below, and select the desired calendar.
You can then optionally select which calendar grouping the calendar will appear in from now on.