With certain places such as: hospital, prison, school or university, the is not normally used, if we are thinking about the idea of such a place and not one in particular.
.
Examples:
She went to hospital in an ambulance.
She has had to stay in hospital for a few days.
My son is going to university in September.
The burglar was sent to prison for 6 years.
My parents go to church every Sunday.
However, if one is talking about visiting one of these places, not actually being part of them, the is used.
Examples:
Peter called in to see his father at the hospital.
The lawyer went to visit his client in the prison.
We went to the school to meet Josie’s teacher.
With Bed, Work & Home
The is not used with bed and work.
Examples:
He goes to bed at 7pm and I read him a story.
I don’t believe it ! It is 11 o’clock and Tricia is still in bed.
My husband is at work, you had better not disturb him.
What time do you finish work on Fridays?
With home, no preposition is used if it is after go, come, arrive orget. However one says at home.