Might sound dull, but I recommend Wikipedia.

There is a word for it, which I forgot, when you look something up on Wikipedia, the article contains a link to another article, and you go, "Oooh, that sounds interesting", open it in another tab, then, when reading the second article, you come across two or three more of such links, and before you know what is going on, you have dozens of tabs open. The only limit is your patience and your computer's RAM.

Eventually you'll end up reading articles that are not even remotely related to your initial inquiry, but highly interesting nonetheless.