If spoken, I think much depends on context as well as tone and inflection and perhaps body language.
If I am a professor or a student and announce "I'm going to
the school" my wife knows exactly where I'm headed.
With "I am going to school" with my briefcase or notebook in hand I'm probably leaving immediately for class.
With a different inflection, saying "I am going to school" at the dinner table I might be announcing a decision to finish my PHD.
Consider "He is going to prison."
To me this can mean the guy has been convicted and is will be taken either immediately or soon to some kind of non-specified incarceration somewhere, perhaps even in another country. It might even be a prediction or threat [if whispered as the jury files in] or if proceeded by something like "I've had enough" [perhaps said with anger] or "well he's done it now". [Sometimes said when discussing politicians or other criminals)
"He is going to
the prison" implies the convicted is headed to a specific prison known to the listener, whether local or implied by location or circumstance (including the type of crime). Or perhaps the subject is known to be a guard or janitor, in which case he may be headed to work.
For me, planning to "go to
the church on Christmas" always implies a specific church while "let's go to church on Christmas" could mean either a specific (our usual) or unspecified church, again depending on context and maybe even whether we habitually go every week or haven't been to church in years. (but better check the schedule - some churches have services Christmas Eve but are closed on Christmas day.
)
If in print, there may be context but other clues will be provided by a good author.
All this is with my own experience having lived and worked in several parts of the US and having read many 100s of books. I know nothing about the rules! (hey, who is this rule-maker?)
JKJ