There is a little tool that is hidden in the help area of Google Calendar. Call it an Easter Egg if you will. It is Google Calendar's Event Publisher.
There are actually two tools on this page; the individual event publisher and an entire calendar publisher.
Both of these tools allow you to create a "Google Calendar" button for an event or an entire calendar. First off these buttons provide a link to an event that you might be promoting or maybe a calendar that you might want people to be able to subscribe to.
But what to do with these buttons. After you insert your information and hit "Create button HTML" you can then use the simple HTML code that is supplied to post an event or an entire calendar to your website. When people click on the button they will launch a Google Calendar window and are asked if they would like to add the event/calendar to their Google Calendar.
You can add this button to almost anywhere you can insert HTML code including a Google Map.
Now someone can add the event to their calendar from Google Maps.
For more information on Google Calendar please check out either of my Google Calendar Training pages at SmallSchoolBigTech.com or at Google Teacher Academy Resources