He looked at the stone figures all around them, breathed deep in the chill of silence of the crypt. (A Game of Thrones)
I think he should have put breathing deeply instead of breathed deep, for two reasons:
first, there is no adjective for the word breathe
second, breathe should be followed by adverb deeply not an adjective deep.
I want to know how this sentence works. How do you explain this condition?
To "breathe deep" is a common idiom, meaning to fully absorb the atmosphere or flavor of a place/event/situation, as well as just to take a deep breath (for instance to calm yourself). Your example is using it in the sense of absorb and connect with the atmosphere. Collins Cobuild has some examples, e.g.
Stand still, breathe deep and you can hear it in your deep heart's core.
I stand on my balcony and breathe deep.
The first here is about breathing deep in the sense of absorbing and connecting with the place or situation and feeling it in your heart - it's more than just a literal deep breath.
For the English learner, there are three issues with Martin's sentence: punctuation; "breathed" vs "breathing"; and "deep" vs "deeply".
"Breathed" here is a simple past tense; it would be more standard to have "and" than a comma before it ("He looked at the stone figures all around them and breathed deep...") but this is literature so you can punctuate how you choose. Here the use of a comma indicates things happening more closely together or at the same time, while "and" might imply things happening one after another.
One difference between "breathed" and "breathing" is that "breathing" implies continuing action, while "breathed" could refer to taking a single breath; "breathing deep" might imply panting.
As to "deep" vs "deeply", both are valid adverbs. English has many pairs like this where something can be an adverb with or without "ly", e.g. quick/quickly. In the idiom "breathe deep", "deep" is common. In other contexts, "deeply" might be more common, e.g. "I love you deeply." But "breathed deeply" would not be wrong - just longer.
In summary it's a combination of a common idiom meaning "to absorb the atmosphere of a place", with simple past tense for completed action, and a comma for speed.
Grammatically, you're correct, but the author here is using breathed deep in a poetic way. Some surrounding text is as follows:
For a moment Eddard Stark was filled with a terrible sense of foreboding. This was his place, here in the north. He looked at the stone figures all around them, breathed deep in the chill silence of the crypt. He could feel the eyes of the dead. They were all listening, he knew. And winter was coming.
This paragraph is describing the crypt, and the phrase "breathed deep" is describing the stone figures, not Eddard Stark's actions. This particular usage is very unusual even for a native speaker, and is done this way intentionally so, to add to the mental imagery that the author is attempting to convey. It helps to understand if you swap "breathed" for "buried", though it loses some of the unusual nuance.
As for using "deep" versus "deeply", that too is a creative choice. "Deeply" is what the reader (and typical grammar) would expect if "deeply" were in reference to Eddard Stark's actions, but by breaking out of expectations with use of "breathed" to account for their presence in the crypt, and following it with "deep", it serves to adjust the purpose of deep/deeply from their depth in the crypt, to how they were breathed into it.
