I've been focused on this question for months and still have no hope of a simple solution. I am SOOOangry at Microshit for providing such a terrible product as Outlook.com. No, there is no "export" option for the calendar although there is a "Share" option. There is apparently no way of backing up the appointment data and so it looks like there is no way to migrate it to anywhere, except the built-in Windows10 Calendar (and I haven't even checked that brainless product out in any detail.) I have resorted to doing a screen print of every month back to April 2010, filing them in a separate folder and printing them and keeping them in a 3-ring binder! Desperate, eh? I have now installed Thunderbird and Lightning and I like what I see so far, but I would really like to get those Outlook.com calendars shifted into Lightning. I could then cut Microsilly loose for good and wouldn't that be just wonderful?