I just read about all the three "de" in Chinese (的，得，地) here in this website :
In the 地's section, it's said that if you use a "straight-up" adverb, you don't need to use 地 at all.
Yet there's this one example sentence which left me confused :
Means : slowly walk.
Now, the question is :
If my memory serves me right, isn't 慢慢 already an adverb that means "slowly"? If that's so, then why in that sentence, 地 is still used after 慢慢?
Plus, if this 慢慢 word turns out to be an exception (like, even though 慢慢 itself is already an adverb, I still need to use 地), is there any other exceptions beside 慢慢?