Fetching details from the dictionary...

prison; jail; gaol
犯人は牢に入れられて反省していた。
The criminal was put in prison and reflected on his actions.
昔の牢は今とは比べものにならない。
Prisons in the old days were nothing like today's.
彼は十年間も牢の中で過ごしたそうだ。
He apparently spent ten years in prison.