[Brainstrom] Extra information widget for certain articles

When I looked at the own blog today I thought what would be cool to add this time! And I thought about a widget that is shown when a certain post is viewed with extra information about that post!

For instance, you have a PR blog about yourself and you go on vacation to Rome. On your blog you create an entry with images and text about you holiday. You mention all the things that you have seen and done. I think it would be nice that when the article is viewed (single.php) an extra sidebar widget would become visible with extra information, that you don’t want to put into the article. Something like historic information about the former Roman Empire, the Vatican etc. Just like a infographic with text and images, next to the entry.

I don’t know if such a widget exists or if anyone mentioned something similar before. Please brainstorm with me how such a widget could be made.

I’m not an experienced php programmeur, but this could be a great opportunity to learn more about it.

Does this already exist? Do you like the idea? What would be needed and where to start?