Depends, the Arch wiki is great, there is/was the German ubuntuusers.de wiki and of course Wikipedia, but none of these are designed to teach you the basics, they are references. By contrast, for tutorials the state of wikis is quite often tutorial 1-3 is great and the rest just missing.

The arch wiki is absolutely incredible. I don't know how they've got it so good, but for a reference of all the things that can be layered upon linux it's amazing.

I haven't checked out Arch's wiki, but the FreeBSD handbook is a similar thing. It's so well documented I use it to compensate for other documentation.

It was a happy day the first time an Arch Wiki link popped up in my Linux Mint google results. That site is crazy good at documenting edge cases and possible bugs.