At the moment I can't think of any instances where you would say 'the nature' but that doesn't mean there aren't any. I'm pretty sure some one will come up with something though. It's an abstract noun, like 'life', so you don't need an article.

Das Leben kann manchmal gemein sein = Life can sometimes be cruel, never 'the life can sometimes be cruel'.

You only need an article when referring to a specific life, e.g. 'The Life of Brian', the same is the case for 'nature' really. I'm not too sure whether you can refer to 'a specific nature' though, rather you'd say something like 'the wildlife in place X is....' etc.