I’ve always liked this particular link. I can pretty much guarantee that there will be at least something on the other end of it that you don’t know.
How do I know that?
Well, that link takes you to a random page on Wikipedia. Since the English version of Wikipedia has over 5 million pages, the chance of you hitting one on a subject about which you have any reasonably complete knowledge is really quite small. (At least, it would be for me!)
So, go ahead, click it and learn something new!
(If, by any chance, you hit a page where you find the subject matter somewhat uninteresting, then you can instead marvel at the fact that somebody found it interesting enough to create a page about it!)