HOSPITAL/THE HOSPITAL, SCOOL/THE SCHOOL, ETC.
Study the following example situation:
James had an accident. He went to hospital.
He had to stay in hospital for many days.
I went to the hospital to visit him.
He got very happy to see me at the hospital.
Someone goes to hospital or is in hospital if he is ill or injured. We are not necessarily thinking of a particular hospital. If someone goes to a hospital as a visitor, then we use the hospital, because we mean a particular hospital (in our example the one where James is).
The same occurs with other places, like prison, school, university, college, church.
A criminal goes to prison (not to the prison), a child goes to school, a student goes to university/college. We do not use the when we are thinking of the idea of these places and what they are used for:
Examples:
After I leave school, I want to go to university (as a pupil).
Why aren't the children at school today? (they are pupils)
Mrs. Jones goes to church every Sunday. (for a religious service)
Mary's brother went to prison for robbery. (he is a prisoner)
Now study the following examples with the:
I have to go to the school to meet my son's teacher. (not as a pupil)
Excuse me, where is the university? (a particular building)
The workmen went to the church to repair the roof. (they didn't go there for a religious service)
Mary went to the prison to visit her brother. (she went there only as a visitor)

