Antimoon is a site for English learners, but the Antimoon Method can be used to learn any language. Of course, you will need to make some tweaks — for example, not every language will require as much focus on pronunciation as English.
If you are interested in specific advice for learning Spanish using the Antimoon Method, you should check out Spanish Only, a relatively new blog written by Ramses, a smart young guy from the Netherlands. Ramses has spent the past few years learning Spanish on his own by immersing himself in Spanish content. The man is full of interesting thoughts and tips, some of which will be relevant to serious learners of all languages.