Is there any way to include external code in sidebar?

Hello all, I am trying to put a list in the sidebar. The list has nothing to do with the content of the site, and is just a list of upcoming events. I haven’t been able to find any plugins that will do that so I am assuming that there aren’t any.

So I was thinking of using an include file (I was just going to create an external html file with the manually updated list). Is there a way to include an external html file into the sidebar?

I would just manually update the sidebar each time, but this is for someone else, and I don’t think it would be a good idea to have them messing around with the sidebar, but they do have basic html skills.

Any help would be greatly appreciated. Thank you very much.